How to retrieve erased text messages

If you have a backup made before you deleted them, you can restore them from that backup:

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

keeping in mind that the restore operation will overwrite all the current data on your iphone. Restore and backup is: all or nothing (you can't restore your messages only).

If you don't have a backup, the deleted messages are gone, sorry.

You can only ask your correspondent to send them back again to your device.

Regards

Giulio