Angular - add option to select on button click

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On my current Angular page I have a select dropdown which is autopopulated with addresses that currently exists for a client, with the final option being "Add New Address". When this is clicked, a modal window is shown where a new address can be entered. When the address is saved it should be added to the dropdown and selected by default.

I've searched online but haven't been able to find anything that worked. Any guidance would be greatly appreciated.

Thanks in advance.

What I have tried:

Currently this is the method that is executed when the new address is saved:
<pre lang="Javascript">addressSubmitted(form: FormGroup) {
    if(form.valid){
      var addressLine1 = form.controls['address'].value;
      var addressLine2 = form.controls['address2'].value;
      addressLine2 = addressLine2.trim();
      var city = form.controls['city'].value;
      var stateId = form.controls['state'].value;
      var state = this.SelectedState; //form.controls['state'].find()
      var postalCode = form.controls['zip'].value;

      var fullAddress = addressLine1 + ', ';
      if('' != addressLine2){
        fullAddress = fullAddress + addressLine2 + ', ';
      }
      fullAddress = fullAddress + city + ', ' + state + ' ' + postalCode
      -->this.popupForm.controls['address_select'].xxxx;
    }
    else{
      this.servicePNotify.error("Error","New address information is not complete");
      this.service.validateAllFormFields(form);
    }

The dropdown in the popupForm form is named address_select and is the control that should have the new address added.