Following comes from Deepak Mittal, Support Escalation Engineer
Tester field in MTM shows different user information.
Please check if there is cache of user information if MTM was installed by other user.
If so, remove the user credential from credential manager by going to Control panel ->User accounts ->certificate manager -> delete the old user.
Note: this is one of the common issues which you can actually face with other products like Team Foundation Server (TFS) as well where client credentials with which products are installed is cached.