Check the Messages app for the conversation thread
Use the Recently Deleted folder in Messages if available
Restore from an iCloud backup made before the texts were deleted
Restore from a computer backup made before the texts were deleted
Check other Apple devices signed in with the same Apple ID
Ask the sender to resend the messages
Contact your mobile carrier to ask about message records
Use a third-party iPhone data recovery tool
Turn on Messages in iCloud to keep texts synced across devices
Back up your iPhone regularly to prevent future loss