To register a new card, you have to do it in the Checkout screen of a booking or activity.
Steps to add a new credit/ debit card
After choosing the club, date and time of your next booking, click on the "continue to payment" button.
To add your card click on the payment method currently showing, and in pop up of option, select "add credit card"
Click on "Pay" again and you will be asked to scan or enter the card you wish to use.
After adding the card information, just click on "Pay". The payment will be made and your booking is confirmed.