<form [formGroup]="addAttributeForm" fxLayout="column">
    <mat-form-field>
      <input matInput formControlName="title" placeholder="Title" required>
      <mat-error>This field is required</mat-error>
    </mat-form-field>
</form>

onSubmit(form: FormGroup) {
  // do work
  form.reset();
}

showForm = true;
formGroup: FormGroup = this.formBuilder.group({
    username: ['', Validators.required],
    password: ['', Validators.required]
});

reset(): void {
    this.showForm = false;
    setTimeout(() => this.showForm = true);
}