If its just one, you just have to declare it for personal use and then you dont have to pay anything. Make sure your luggage does not have any other electronic item at that time.
You can also open it here and pack it again. Remove the stickers etc inside and declare it as used as well. If they ask, tell them you were using it here for a couple of months and now you dont need it here any more so you brought it back to Pakistan.
However no duty on new screen as well since you are taking it for your personal use and not for resale purpose.