If you would like to add an alternative card:-
Tap 3 lines (menu) at the top of 'Home' screen
Tap - Manage Cards
Select + and add card number, Cardholder name, expiry date and CVV
Tap - Save Card
By tapping the card you can set it as your default payment card.
If you have more than two cards you can delete one by pressing "x" and selecting "Delete". You cannot delete your default card.