iMessage

If you were syncing Messages with iCloud and deleted them, they can't be recovered. If you weren't syncing Messages with iCloud, do you have a backup you can restore from? Restoring from a backup erases all data currently on your device. Any data newer than when the backup was made will be erased. A restore is an all or nothing restore. You can't access a backup and only restore certain files.

Backup - Restore your device from an iCloud or iTunes backup.    

See How to retrieve deleted text messages on iPhone

https://www.macworld.co.uk/how-to/iphone/retrieve-deleted-texts-iphone-3636380/ and

How to Recover Deleted Text Messages on Mac https://www.ibeesoft.com/recover-mac/recover-deleted-messages-imessages-mac.html