Additional sign-in or account-related issues within Microsoft Teams Free
Hello
Is it because you don't have access to the device, but Teams is signed in with your account there?
I saw you selected Teams free, so I believe this is personal Microsoft account?
If so, go to https://account.live.com > Security > Manage how I sign in, scroll down and click on sign out everywhere. This will eventually sign you out of Teams on that device, but it can take up to 24 hours, it is not immediate.
If you worry about your account being compromised, you might want to also consider password change.