Know who is filling form Angular 6

I'm making an application where you can see things related to your car, an Agent can have a list of clients and each client must fill a form to share details of the car that is in the shop. This form is accesible to both agent and client and they can change answers. Considering this, I need to know who made a change in the questions of the form. Is there any way to achieve this with Angular forms?

The questions in the form are formatted like this:

      <p>How old is your car?</p>
        <mat-form-field>
          <input 
          type="number" 
          matInput 
          name="clientCarAge" 
          [(ngModel)] ="model.clientCarAge"
          >
          <span matSuffix>years old.</span>
        </mat-form-field>

I think that a property like answeredBy must be implemented but I'm not sure how.