Hello Nilufar,
You can delete these tickets by using the generic agent.
Move all tickets which should delete in a queue, e.g. Junk.
Open the generic agent menu in the admin area and create a new job.
Open the „Select Tickets“ area and choose the queue which contains the tickets you want to delete.
In the area „Execute Ticket Commands“ you can choose „yes“ at the point „Delete tickets".
After youre saved the changes you can Run the task.
Bye, Tino Voigt