Open the Messages app
Tap Edit or Filters if available
Tap Recently Deleted
Select the messages or conversations you want to remove permanently
Tap Delete
Tap Delete Messages to confirm
If Recently Deleted is not available, go to Settings
Tap Apps
Tap Messages
Tap Keep Messages
Choose a shorter retention period if needed
Delete the conversation from Messages if it still appears
Restart your iPhone if deleted messages still show up
Check iCloud Messages settings if messages keep returning
Turn off Messages in iCloud if needed
Delete the messages from other synced Apple devices too