Hold prevois selected option in a variable preState and revert newState to preState when user clicks no.

export class AppComponent  {

  state;

  newState;

  preState;

  checkState = false;



  options = [

    {name:'dormant'}, 

    {name:'active'}, 

    {name:'finished'}

  ];



  setState(state) {

    this.preState = this.newState;

    this.newState = state

    this.checkState = true;

  }



  selectedOption(option) {

    return this.newState === option;

  }



  yes() {

    this.state = this.newState;

    this.checkState = false;

  }



  no() {

    this.checkState = false;

    this.newState = this.preState;

  }

}

UPDATE:

To show the disabled option mentioned in your UPDATE, put [selected]='!newState' on the disabled option:

<select (change)=setState($event.target.value)>

  <option disabled [selected]='!newState'>--Pick an option--</option>

  <option *ngFor=let option of options [value]=option.name [selected]=selectedOption(option.name)>{{option.name}}</option>

</select>



<div *ngIf=checkState class=check-state>

  <p>Are you sure you want to change</p>

  <p><span class=bold>{{state}}</span> to <span class=bold>{{newState}}</span></p>

  <button (click)=yes()>yes</button><button (click)=no()>no</button>

</div>