Question about Account Switch

Hello, I had a quick question for the iOS version of the game. My little brother wants to log into his account but he can't. I want to log out of my account but when I uninstall the app from the store, it keeps my account.
Could someone tell me how to logout of my account so that my brother can get on his?
If someone could please reply back that would be great!
Thanks
and also our family loves this game!!!
  

My brother created the account at a friend's house and he wants to login on my iPhone?
Is there a way to do this?

Hello !

No it's not possible. The rule is : "One account, one device"

Ok, thats fine, thank you!