Check the Recently Deleted folder in Messages
Open Messages
Tap Edit or Filters
Tap Show Recently Deleted
Select the messages
Tap Recover
Restore from an iCloud backup
Go to Settings
Tap General
Tap Transfer or Reset iPhone
Tap Erase All Content and Settings
Set up your iPhone again
Choose Restore from iCloud Backup
Restore from a computer backup
Connect iPhone to Mac or PC
Open Finder or iTunes
Select your iPhone
Choose Restore Backup
Check other Apple devices
Open Messages on iPad or Mac
Look for the deleted messages if Messages in iCloud is enabled
Ask the sender to resend the messages
Contact your carrier if SMS backup or message recovery is available