It is installed when T-Mobile remotely accesses your phone for troubleshooting when say, you call in with a tech issue. Also check your My T-Mobile app as there are settings there that allow remote diagnostics. I have noticed this same issue before and was able to uninstall/remove the app. Read the fine print in the app...it means you agree and give permissions to access certain parts of the OS and phone info. Typically, they cannot access the private spaces or files, but do know how much space, storage, memory, number of apps, etc.... like that.
Manage your T-Mobile account