[Inquiry] Please provide clarification on "Link a Device"

Usually when you delete and reinstall the app it will start as if you are a new player and you can play as a guest. Though after this screw up it is not working in that way for some reason whereas when I had to reinstall earlier to fix the crashing from new update it did start me off as a guest before I clicked the "Have an account?" button. For iOS I do not think you can sign out of Game Center like you can on Android with Google Play unfortunately for whatever reason or else I would have done that :(