Microsoft Teams insists on signing me into an org I am no longer part of, signs me in as a guest

This question has been asked before, but none of the answers provided have worked for me.

My wife and I share our Microsoft365 account. A few years she worked for an org that used Teams for meetings, so they gave her credentials to sign into their org, which she did until she quit. So, those credentials are no longer valid.

When I sign into Teams using the app on my laptop, it shows that old org's name up top and shows me as a guest. I did the procedures of removing the credentials using Credential Manager, deleting Teams' cache, and resetting Teams. No change.

If I sign in via my browser, after entering my credentials, a window appears allowing me to choose between my personal account and that old org's account. If I choose my personal account, Teams logs me on with my profile. Great. But the app does not do that on my computer.

When I sign in using the app, the old org's name appears up top followed by a red triangle. When I click on my guest profile, the drop down shows the name of that org, also with a warning triangle. Once in the past I did click on that org's name to see if I could sign out, but since the credentials were no longer valid, that did not work.

If I sign into Teams on my phone, it also shows me the page allowing me to choose between my personal account and that org's account.

All I want is to remove that old organization's account from my computer, and signing into the Teams app as the account owner, not a guest, since I might be joining a new organization and take calls from them. Please help.