How do I find my game ID?
You can do the followings: click your image>setting>account, then you can find your game ID.
How do I switch between accounts?
Your can easily switch your account as long as it is linked to a Google or FB account! (IOS users can also bind account with apple account) Remember that each ID can only be linked to one Google or FB account.
You can click your image>setting>account>switch account to switch.