use formatDate method

app/Http/Controllers/TasksController.php

@@ -158,6 +158,8 @@ class TasksController extends Controller
                   'name' => $user->name,
                   'lastname' => $user->lastname,
                   'taskName' => $task->name,
+                    'start' => $event->start,
+                    'end' => $task->end,
                 ];
                 Mail::to($user->email)->send(new TaskParticipationCancelledMail($data));
             }