I have seen several members struggling to update the Zwift app on Apple TV. The same happend to me.
When asked to update the Zwift app you are asked to agree to terms and conditions, however, after clicking OK, a message shows up saying: " coming soon". The only solution has been to delete the app and reinstall, which is more or less infeasible due to the frequent updates of the Zwift app.
After a lot of research, I found out that the problem most likely is related to a bug where Apple doesn’t register that terms and conditions have been accepted. However, this can be accepted in other ways than in the Zwift app.
I have only used the Apple TV for Zwift and therefore not used any of the other apps which may be a part of the problem.
So my solution was to open the Apple Music app on the Apple TV and sign up for a free trial. After signin up, you are asked to accept T and C. You are then asked to give payment information but I just opted out of this option.
After this, it is possible to update the Zwift app.