On iPhone, open TestFlight, choose the Interrail app and tap Stop Testing. On Android, open the testing link again, or go to the app’s page in Google Play, and choose to leave the programme.
If your Pass is in the new app and you want to use it in Rail Planner again, contact Customer Service first so they can unlink it. Your start date and used travel days are kept, but your trips won’t sync, so you’ll need to plan them again (see “Something has gone wrong with the beta”).