Retrieving deleted messages on message

Hello,

Go to Settings > your-name > iCloud > Messages. Is it on? if yes, there is not much that you can do (perhaps contact the other party and see if they have it).

If Messages is off, you can get it back by restoring from a backup that contained it:

Restore your iPhone, iPad, or iPod touch from a backup

Good luck.

Deleted means gone for good.