how do i change monthly charge for apple TV to yearly

See the following from https://9to5mac.com/2021/06/30/how-to-save-money-when-buying-apple-tv/

To subscribe to Apple TV+ yearly, first sign up normally. After you have signed up to the monthly plan, go to your Settings on your iPhone or iPad. Select Apple ID -> Subscriptions. Tap on Apple TV+. On this screen, you will be able to switch from Apple TV+ monthly to Apple TV+ yearly.

Go to your subscriptions overview, select the Apple TV+ subscription, see under Options: monthly (1 Month) will have a checkmark, tap yearly (1 Year) to change that.