If you're using a web-wallet, please navigate to Settings - General - Linked Banks/Cards.
If on mobile app, please go to Settings in the top left corner and scroll down till you see Linked Banks/Cards sections.
From here, you can link or remove your bank accounts or cards. Once you add a card or bank account, your Blockchain.com Wallet will remember it for future purchases.
Note: At this time, you may add up to 10 cards (maximum) to your Blockchain.com Wallet Account.