To change your credit card for Mozilla VPN, open the Mozilla VPN app, go to Settings, select “account”, then "manage subscription.” From there, update your credit card information under “paid subscriptions” by clicking "manage" to change your card details. Hope this helps.

I need to change my credit card for Mozilla VPN. How do I do that? Pieter de Haan

See https://support.mozilla.org/en-US/kb/how-do-i-update-my-payment-information-mozilla-vpn

Btw this section you posted in is for support of (desktop) Firefox.

The place you get support for Mozilla VPN is at https://support.mozilla.org/en-US/questions/new/firefox-private-network-vpn