Check the “Recently Deleted” or “Trash” folder in your Messages app (if available)
Restore from a cloud backup (iCloud/Google Messages backup) if you have one from before deletion
Restore from a full device backup using your computer backup tool (iTunes/Finder for iOS, Samsung Smart Switch/Google backup for Android)
If using a carrier-based backup or sync service, restore messages from that service’s web/app interface
Use your device’s message sync settings to confirm whether deleted messages were synced from another device
Contact your mobile carrier to ask whether they retain message content (often they do not)
If you have end-to-end encryption and the other party still has the messages, ask them to resend/copy the content
Consider third-party data recovery tools only if you understand the risks and limitations (results vary and may require forensic access)
Avoid overwriting data after deletion (don’t reinstall apps or perform actions that may overwrite storage)