I know this is kind of old question, but I would love to add the answer.

<select class='select-option' 
        (change)='onOptionsSelected($event)'>
    <option class='option' 
    *ngFor='let option of dropDownData' 
    [value]="option.seo_val">{{option.text_val}}</option>
</select>

onOptionsSelected(event: Event): void {
  const value = (event.target as HTMLInputElement).value;
  console.log(value)
  ...
}

Thank you Enjoy