Since no one responded I took it upon myself to investigate and found the solution.
- Select T-Mobile app
- Force stop
- Three dot settings at top-right
It doesn't actually uninstalls, but does clear all data from the app. From there you will just "re-create" your account. I use quotes because I already had an account, I just entered my info and now it works.
So glad to see that you found a solution! I'm going to go ahead and mark it as correct in case someone else winds up with the same question!