Check the Recently Deleted folder in Messages
Open Messages
Tap Edit or Filters
Tap Recently Deleted
Select the messages
Tap Recover
Restore from an iCloud backup
Go to Settings
Tap your name
Tap iCloud
Tap iCloud Backup
Erase and restore your iPhone from the backup that contains the messages
Restore from a computer backup
Connect your iPhone to a Mac or PC
Open Finder or iTunes
Select your device
Restore from the backup that contains the messages
Check other Apple devices
Open Messages on your iPad, Mac, or another iPhone
See whether the messages are still there
Ask the other person in the conversation to resend the messages
Contact Apple Support if the messages were deleted recently and you need help checking recovery options