During the loading screen, a “Switch Account” option will appear in the top-right corner. If you tap it before the game fully loads, you’ll be signed out and prompted to log in again ...

Disabling your Twitch account effectively deactivates your account, but doesn't delete your user information. Plus, if you change your mind later, you can log back in to reverse the process.

double-check that the "Account to delete" box has the right username in it (this is added automatically and can't be changed unless you change account). You then have the option to tell Twitch ...