Follow the below steps:
Log into your PayFast account
Navigate to the Transactions tab and click on "Subscriptions"
Under "Your Subscriptions"find the subscription that you want to edit the card on
Under "Actions" click on the "card" icon to edit the card
Select the card you would like to change the subscription to, or if you want to add a new card click on the "New Card" option. If you add a new card you will then need to repeat steps 2-4.
If you have any queries about this, please contact Payfast on email@example.com or call them on 0861 729 327.