Unable to Login, because Code can't received via Auth-App, because I needed to install the App on a new Phone

I am unable to log in anymore because, after reinstalling the Auth app, I have no way to set up my accounts again. Whenever I try to log in on the Microsoft site, the system sends a code to the app. However, I can’t access it anymore. The IT department of my school says they can't help me because they don't support the Microsoft Auth app. I am currently helpless as there is nothing I can do