Please help me!!!

I updated my iOS and now I can’t get into my account! My username is Bowserboy44, I can’t log in and it says “It’s already registered on another device” and that’s total bull crap. Please help me! I will give the app five stars once it’s back, this is one of my favorite apps, can a developer please respond and tell me how to fix this?

Bowserboy44 about Quidd: Digital Collectibles, v1.10.3