modal-example-size.html

<button class="btn btn-primary" (click)="smallModal.show()">Small Modal</button>
<ng-template nzbModal #smallModal="nzbModal">
  <div class="modal fade" tabindex="-1">
    <div class="modal-dialog modal-sm" role="document">
      ....
    </div>
  </div>
</ng-template>


<button class="btn btn-primary" (click)="largeModal.show()">Large Modal</button>
<ng-template nzbModal #largeModal="nzbModal">
  <div class="modal fade" tabindex="-1">
    <div class="modal-dialog modal-lg" role="document">
      ...
    </div>
  </div>
</ng-template>