If you have been added to another organisation’s team as a Guest and you no longer need access to it, or perhaps your team access has been revoked, but their Teams organisation showing in your list of accounts, you can remove yourself from them.
To do this, first click Manage Account from the drop down menu that appears when clicking on your avatar
From the Settings popup, click on the Manage button next to your identity
This will open your Microsoft Account profile settings page. From there, choose Manage Organizations
From the list of other organisations, find the organisation you want to remove yourself from and click Leave Organization
Follow the on screen login prompt and then when the confirmation modal pops up, click Leave
If this doesn’t work, the IT admin of the other organisation will have disabled your account for sign-in on their side. If this is the case, you will need to contact the partner’s IT support to request your guest account is deleted manually.