How do I retrieve deleted text messages?

That would ONLY apply if the OP doesn't have messages turned on in iCloud.

If you go to Settings > Your Name, Apple ID, iCLoud, iTunes & App Store

Tap iCloud

If Messages are turned on, when you delete the message it's deleted and it's deleted everywhere you have iMessage on.

Do you have any other Apple devices that share the same messages? Usually messages will still be saved on other devices.