array_add method In laravel

i try to use array_add method to add new element to array in for loop

 public function getNotArray() {   

   // looping over $service Object
for($x = 0; $x < count($service);$x++) {

  $firstService[$x] = $service[$x]->first_date_for_service;

        while (Carbon::now() > $firstService[$x]) {

            $firstService[$x]->addMinutes($service[$x]->notification_period);

    if($firstService[$x] < Carbon::now() && $firstService[$x] > $service[$x]->serviceHistory->where('status','done')->max('created_at')) {

      $arr[] = array_add($service[$x],'notificationDate',date($firstService[$x]));

            }
        }

    }
    return  $arr;
   }  

The above script working well ,but return notificationDate fixed value when loop over $arr

i need to get notificationDate according for value that $firstService[$x] carries in each loop

Any Suggestions,Thanks

via Chebli Mohamed