Your post is a bit confusing. This is the apple Account forum, but you are referring to Apple Pay. Which is it? Those are 2 different things and will have different ways of modifying billing addresses. Though in both cases billing addresses are tied to the specific payment method, not your account in general.
If you made a purchase using Apple Pay, then your Apple Account's payment methods are not involved and a such any billing addresses there are not relevant to the purchase.
To edit Billing Addresses for Apple Pay, you open the Wallet App, select a card or payment method there, tap on the (...) icon at the top, and then on Billing Address. You can choose a different one from the ones listed, edit them by tapping on Edit at the top, and then on a specific address you wish to change, or add a new one by tapping on "Enter new Billing address".
click here ➜ Change or remove the payment cards that you use with Apple Pay (update billing information) - Apple Support
If this is in relation to purchases made with payment methods on your Apple account in Apple's online stores like iTunes, App Store, Books Store etc... then you can change the billing address for the specific payment method used in Settings ➜ Account ➜ Payment & Shipping ➜ Tap a Payment Method ➜ Tap Edit.
click here ➜ If you need to change or update your Apple Account payment method - Apple Support
*These steps all assume an iPhone or iPad.
