I am playing as guest on iOS and trying to register. What is the 'preferences app'?

You have to log into your Game Center account and then launch the game again.
If you have any other questions or problems, don't hesitate to contact our Customer Support.

Please, keep in mind that if you will not register your account/delete app cache or reinstall the game you might lose all of your progress 

We aren’t storing guest accounts in our database