How to show required error on mat-select, on clicking next form

Question

So i have a dropdown first. Then i have a input. When i select the input without selecting the first dropdown, i need to show validation for the first drop down.

1.First form:

       <mat-select
          formControlName="client"
          multiple
          class="custom-select-csRp"
          panelClass="custom-select-panelCsrp mat-select-custom scrollcsrp"
          disableOptionCentering
          #selectcsrp
          contentTabIndex="null"
          (openedChange)="panelOPened()"
          #matSelect
          (selectionChange)="matOPtionChanged($event)"
        >
          <mat-option #allSelected [value]="0"> All </mat-option>

          <mat-option *ngFor="let list of clientList" [value]="list">
            {{ list }}
          </mat-option>
        </mat-select>     
   

2.Second form :

          <div class="access-type-text ipHeading">Entity ID</div>
            <div
              [ngClass]="{
                'is-empty': !createRAForm.get('entityIDControl').value
              }"
              class="form-group label-floating"
            >
              <label class="control-label" for="entityId">Entity ID</label>
              <input
                class="form-control ipFields"
                id="entityId"
                type="text"
                name="entityId"
                formControlName="entityIDControl"
                (keyup)="ipFieldEnable($event, 'entityIDControl')"
              />
          </div>