It is very easy. All you need to do is uninstall the Grindr Beta app like other apps on iOS. Of course, you are free to re-install a Beta version from Testflight app again.
It is advised that you must uninstall the Beta version app before you reinstall a production version app from the App Store to avoid previous data synchronization issues.
- Don't forget to backup your chats before switching from Beta to productions versions or vice versa!