Where can I find Netflix, Disney, etc. in the MagentaTV app on my Fire TV Stick?

Hello, I booked MagentaTV yesterday, including Netflix, Disney+, and RTL+. Now I want to stream the whole thing using the MagentaTV app on my Amazon Fire TV Stick. However, I read on the website that if I want to log in or watch Netflix or Disney, I always have to do it using the Magenta app, otherwise my existing subscriptions will be renewed at the old price. Unfortunately, I can't find my streaming providers in the Magenta TV app on my Amazon Fire TV Stick. Can anyone tell me where I can find the providers in the app or how I can stream the external providers using the app on my Fire TV Stick? Thanks 🙂