I need to update my default shipping address

There are several accounts, not to mention credit and debit cards, that may want an updated address. This is the Apple Card MasterCard community, so I’ll share the link to edit your information for that account. If you can share additional details in regard to what addresses you want to change.

Update your Apple Card account information - Apple Support

All you need to do, is to go to your iCloud then the payment and shipping fee. You click on it, to update your billing info.

Unfortunately, that does not update your Apple Card MasterCard address.