Dynamically changing database while requesting on custom route file

Question

I am struck into strange problem. My problem is I am trying to save data into another database which is quite easy only If I have register that request route in web.php file.

But If I register custom route file in RouteServiceProvider.php and the request route through which I am trying to enter the data into different database is in that route file then it dosen't change the database connection. i am using Laravel version 5.7

Here is the code.

\Config::set('database.connections.user_databases',
        [
            "driver" => "mysql",
            "host" => "127.0.0.1",
            "database" => 'testingdatabase',
            "username" => "root",
            "password" => "ahmedalvi666"
        ]
    );

    $userNew = new \App\User();
    $userNew->company_name = $request->company_name;
    $userNew->password = $request->password;
    $userNew->last_name = $request->last_name;
    $userNew->first_name = $request->first_name;
    $userNew->email = $request->email;
    $userNew->created_at = date('Y-m-d H:i:s');
    $userNew->updated_at = date('Y-m-d H:i:s');
    $userNew->save();

Into User.php file I have set connection to user_databases