Sorry I'm not the one who can give any info on that since I too play with a guest account. I didn't link mine. If you haven't checked out the post by Vinikiss here it is:
1. FIRST OF ALL, use the official app and log in your account. After the message showing the successful log, click ok (or not) and CLOSE THE APP IMMEDIATELY, DO NOT CONTINUE and uninstall it.
2. Install the app provided here, DO NOT START BY TAPPING IN THE MIDDLE OF THE SCREEN, instead, click ACCOUNT LINK on the bottom right and you'll be able to link your account.
It works, I've done it many times. If you get any error, clean your cache and repeat the steps.