How to use fragments with navigation drawer? (Java)

Question

I am using a navigation drawer, in it I have a button that I want to put a specific fragment in the "fragment container" but I do not know how to make it place, the tutorials that I have seen show in past versions and I do not understand how to use the navigation drawer . This is the button: private Button bAdmin, I want to put this fragment by pressing the button: AdminFragment.java / admin_fragment.xml

Fragments are controlled from mobile navigation:

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/mobile_navigation"
app:startDestination="@id/nav_inicio">

<fragment
    android:id="@+id/nav_inicio"
    android:name="com.example.donmigue.ui.inicio.InicioFragment"
    android:label="@string/menu_inicio"
    tools:layout="@layout/fragment_inicio" />
<fragment
    android:id="@+id/nav_comprar"
    android:name="com.example.donmigue.ui.pedido.PedidoFragment"
    android:label="@string/titulo_f_pedido"
    tools:layout="@layout/pedido_fragment" />
<fragment
    android:id="@+id/nav_menu_combos"
    android:name="com.example.donmigue.ui.combos.CombosFragment"
    android:label="@string/titulo_f_combo"
    tools:layout="@layout/combos_fragment" />
<fragment
    android:id="@+id/nav_menu_emp"
    android:name="com.example.donmigue.ui.emp.EmpFragment"
    android:label="@string/titulo_f_emp"
    tools:layout="@layout/emp_fragment" />
<fragment
    android:id="@+id/nav_menu_bebidas"
    android:name="com.example.donmigue.ui.bebidas.BebidasFragment"
    android:label="bebidas_fragment"
    tools:layout="@layout/bebidas_fragment" />
<fragment
    android:id="@+id/nav_cuenta_editar"
    android:name="com.example.donmigue.ui.perfil.PerfilFragment"
    android:label="@string/label_titulo_perfil"
    tools:layout="@layout/perfil_fragment" />
<fragment
    android:id="@+id/nav_cuenta_pedidos"
    android:name="com.example.donmigue.ui.mPedidos.MisPedidosFragment"
    android:label="mis_pedidos_fragment"
    tools:layout="@layout/mis_pedidos_fragment" />
<fragment
    android:id="@+id/a_ProductoFragment"
    android:name="com.example.donmigue.ui.AProductos.A_ProductoFragment"
    android:label="a__producto_fragment"
    tools:layout="@layout/a__producto_fragment" />
<fragment
    android:id="@+id/a_ClientesFragment"
    android:name="com.example.donmigue.ui.AClientes.A_ClientesFragment"
    android:label="Clientes"
    tools:layout="@layout/a__clientes_fragment" />
<fragment
    android:id="@+id/a_PedidosFragment"
    android:name="com.example.donmigue.ui.APedidos.A_PedidosFragment"
    android:label="a__pedidos_fragment"
    tools:layout="@layout/a__pedidos_fragment" />
<fragment
    android:id="@+id/AdminFragment"
    android:name="com.example.donmigue.ui.Admin.AdminFragment"
    android:label="ADMINISTRADOR"
    tools:layout="@layout/admin_fragment" />
</navigation>

This is the code of the activity where I control in navigation drawer:

private FirebaseAuth mAuth;
private DatabaseReference fireData;
private AppBarConfiguration mAppBarConfiguration;
private TextView userName;
private Button bAdmin;
public static Activity PageA;

@Override
protected void onCreate (Bundle savedInstanceState) {
    super.onCreate (savedInstanceState);
    PageA = this;
    mAuth = FirebaseAuth.getInstance ();
    fireData = FirebaseDatabase.getInstance (). getReference ();
    setContentView (R.layout.activity_pagina);
    Toolbar toolbar = findViewById (R.id.toolbar);
    setSupportActionBar (toolbar);

    DrawerLayout drawer = findViewById (R.id.drawer_layout);
    NavigationView navigationView = findViewById (R.id.nav_view);
    // Passing each menu ID as a set of Ids because each
    // menu should be considered as top level destinations.
    mAppBarConfiguration = new AppBarConfiguration.Builder (
            R.id.nav_inicio, R.id.nav_comprar, R.id.nav_menu_combos, R.id.nav_menu_emp, 
            R.id.a_ClientesFragment, R.id.AdminFragment,
            R.id.nav_cuenta_editar, R.id.nav_cuenta_pedidos, R.id.nav_menu_bebidas)
            .setDrawerLayout (drawer)
            .build ();
    NavController navController = Navigation.findNavController (this, R.id.nav_host_fragment);
    NavigationUI.setupActionBarWithNavController (this, navController, mAppBarConfiguration);
    NavigationUI.setupWithNavController (navigationView, navController);
    navigationView.setItemIconTintList (null);

    View hView = navigationView.getHeaderView (0);
    userName = (TextView) hView.findViewById (R.id.navHeader_name);
    bAdmin = (Button) hView.findViewById (R.id.btnAdmin);
    getUserInfo ();

    bAdmin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            //PLACE THE FRAGMENT ADMIN
        }
    });
}

@Override
public boolean onCreateOptionsMenu (Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater (). inflate (R.menu.page, menu);
    return true;
}

//SIGN OFF
public void Close Session (View view) {
    mAuth.signOut ();
    Intent intent = new Intent (this, LoginActivity.class);
    startActivity (intent);
    finish ();
}

// GET AND PLACE USER INFORMATION
private void getUserInfo () {
    String id = mAuth.getCurrentUser (). GetUid ();
    fireData.child ("Person"). child (id) .addValueEventListener (new ValueEventListener () {
        @Override
        public void onDataChange (@NonNull DataSnapshot snapshot) {
            if (snapshot.exists ()) {
                String name = snapshot.child ("name"). GetValue (). ToString ();
                userName.setText (name);
                String value = snapshot.child ("value"). GetValue (). ToString ();
                if (valor.equals ("1")) {
                    bAdmin.setVisibility (View.VISIBLE);
                } else if (valor.equals ("0")) {
                    bAdmin.setVisibility (View.INVISIBLE);
                }
            }
        }
        @Override
        public void onCancelled (@NonNull DatabaseError error) {

        }
    });
}

@Override
public boolean onSupportNavigateUp () {
    NavController navController = Navigation.findNavController (this, R.id.nav_host_fragment);
    return NavigationUI.navigateUp (navController, mAppBarConfiguration)
            || super.onSupportNavigateUp ();
}

@SuppressLint ("WrongConstant")
public void showSelectedFragment (Fragment fragment) {
    getSupportFragmentManager (). beginTransaction (). replace (R.id.nav_controller_view_tag, 
    fragment)
            .setTransition (FragmentTransaction.TRANSIT_ENTER_MASK)
            .commit ();
}

@Override
public boolean onNavigationItemSelected (@NonNull MenuItem item) {
    return false;
}