Gorovalo

import { FormGroup, FormBuilder } from '@angular/forms';

@Component({
...
})
export class ComponentName {
form: FormGroup;
  
constructor(
    private fb: FormBuilder
  ){
   this.form = this.fb.group({
    test3: [...]
});
}
}

setSelect(event) {
  this.form.controls['test3'].setValue(event);
}

@Component({
  selector: 'parent',
  template: `<section>
  <my-cool-child-component [state]="someData"></my-cool-child-component>
  <button (click)="clickMe()"></button>
</section>`,
  styles: ``,
})
export class ParentComponent  {
someData; 

 clickMe() {
            this.someData = ...;
  }
}

import { Input } from '@angular/core';

@Component({
  selector: 'my-cool-child-component',
  template: `<div><h1>{{state}}</h1></div>`,
  styles: ``,
})
export class MyCoolChildComponent  {
  @Input() state;
}