How can I change my Apple billing address to a different country?

John,

Also see the info in here, including what to do if there is a problem changing:

Change your Apple ID country or region - Apple Support

Sign in to your Apple ID account page and edit / update your Apple ID details.

https://appleid.apple.com

-> edit your billing addres.

OR

1. 

To change the billing address you can do (macOS & Windows OS) via iTunes

Start Music -> Click on iTunes -> side bar click iTunes Store -> go to Account (top bar) -> View Account -> Sign in -> Apple ID Summary -> Billing Address -> Edit.

2. 

(iPhone & iPad) Go to -> Settings -> tap your Profile -> Payment and shipping -> Change Address.

Edit the Address -> tap Done.