how to retrieve deleted text messages

You don't, unless that was the last time that you backed up your iPhone. The only way to retrieve a deleted text is to restore your phone to a backup that was made while the message was on the device. Since the iPhone overwrites the backups each time you take one, then that would have been overwritten by however many times you have made backups since that date. Remember also, restoring to a backup deletes everything on the device and restores it to the date/time of the backup. Anything done since that date is lost.

If you have a back up that contains the messages, you can restore the phone from that back up. Note that restoring your phone from a back up will overwrite everything currently on the phone.