i have back up messages on i cloud how do i retreve them

If you were using messages in iCloud - Keep all your messages in iCloud - Apple Support, then those messages aren't considered a part of the backup. If you weren't using this feature, you can restore from a backup.

The only way of recovering a deleted text message is on the off-chance you had a back-up stored which included this text message however that would mean erasing your phone and setting it up with the new back-up, which can be very time-consuming, plus you need to be confident your text message is actually in this back-up and you have one in the first place.