I used my Google account to initially log in but that is my wrong account. I wanted to log in with my other account but the app always automatically logs me back in with my Google account when I revisit the login page.
Wouldn't logging out of SE, logging out of Google and then logging back in to SE work. Delete your cookies for SE/SO/Etc.com from the browser you want to use or try a different browser on your phone.
See also: "Use your Google Account to sign in to other sites or apps":
Remove a site or app with access to your account
- Open your Google Account. You might need to sign in.
- Under "Sign-in & security," choose Apps with account access and then Manage apps.
- Choose the site or app you want to remove.
- Choose Remove.
Note: If you remove account access from a third-party site or app, it may retain information you provided from:
- When you signed in with your Google Account
- When you granted additional Google Account access to the app or site
Those last two points means Google doesn't obligate the site to erase everything, but the site won't have permission from Google Sign-In and so a properly working website ought to require you to authenticate yourself by email and password or one of the other 3rd party authenticators.
See also: Login with a different Google account .
How do I change my OpenID provider(s)?
Help Center: "How do I add or remove login credentials from my account?".