Zip associates your card with your order when you first complete the checkout process. If you need to change which payment method is used for future installments for an order, follow these steps to associate a different card with a given order. This will cause all further installments for that order to be billed against your new card.
Log into the Customer Portal at https://customer.us.zip.co/en-US/login.
Go to the Orders Page and click View Order for the order you would like to change. Click Edit next to the payment card, select the card you’d like to use, and click “Use this Card"