Check the Recently Deleted folder in the Messages app
Open Messages
Tap Edit or Filters
Tap Show Recently Deleted
Select the deleted iMessages
Tap Recover
Check iCloud backup
Go to Settings
Tap your name
Tap iCloud
Tap iCloud Backup
Restore from a backup that may contain the deleted iMessages
Check another Apple device
Open Messages on your iPhone, iPad, or Mac
See whether the iMessages are still synced there
Check Messages in iCloud
Go to Settings
Tap your name
Tap iCloud
Tap Messages
Confirm whether Messages in iCloud is enabled
Check email notifications
Search your email inbox for iMessage notification emails if they were enabled
Check with the other person in the conversation
Ask them to resend the messages if needed
Check third-party backup tools
Review any backups made with Finder, iTunes, or other backup software
Contact Apple Support
Ask about recovery options for deleted iMessages