Hello!
You can now change your card details securely in-app (you may need to force-reopen it); this was long-overdue! You can do so under the Account Tab > Billing > Card.
We decided not to add any extra steps before you can change them, but will have Touch/Fingerprint/Face ID unlock for the app by the end of the week. We were worried about refunding to a separate card, but this isn’t possible anyway – a refund is always sent to the original payment method.
I’m sorry about the lack of public updates recently – we’ve now committed to a regular schedule, and look forward to closing out the year with as much as we can fit in! 
Have a great evening,
Nick