4kappletv
When I set up the Apple TV 4K, it was possible that the Internet speed was slower than usual, and Apple TV 4K said it is not possible to play at 4K for the iTunes movies that I purchased.
But what if I stop all other Internet connections, and want Apple TV 4K to re-try to see whether it can use 4K as a default (or that I don't mind the movie being choppy once in a while), how can that be done?
I had something similar happen with a rented film.
The only thing that I can recommend that you try is that you contact the iTunes store customer support and explain your issue, they will most likely give you a refund and you can delete the movie and try re-purchasing it.
Try restarting your Apple TV.
Hold down the Home and Play buttons on the Siri remote, or hold down the 'down' button and the menu buttons.
Images below
The light will flash quickly, then let go of the buttons. You will see the apple logo.
Try watching your movies now!
I hope this works for you!
Best Answer
The Apple TV estimates bandwidth available every time you play a movie - so it is done automatically. There's no need to rerun the setup process whenever the load on your internet connection changes.