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 your name
Tap iCloud
Tap iCloud Backup
Erase the iPhone
Set up the device again
Choose Restore from iCloud Backup
Restore from a Mac or PC backup
Connect the iPhone to a computer
Open Finder or iTunes
Select the device
Choose Restore Backup
Check other Apple devices
Open Messages on your iPad or Mac
Look for the missing conversation
Copy or save the messages if needed
Ask the sender to resend the messages
Request screenshots or copied text if recovery is not possible