1.) In the Asana Web App (https://app.asana.com), go to "My Profile Settings" -> "Apps" and hit the "Deauthorize"next to "Asana for Microsoft Teams" 2.) Try to add an Asana tab in Microsoft Teams. You should be presented with a login prompt asking to grant certain permissions. Click "Not You" in the bottom of the login prompt and you will be able to log in as another account.
If that doesn't work, try also logging out of the Asana Web App in between steps 1 and 2. Hope that works!