To set another card as default card, you will first need to add a card, click on the link below if you require further instructions: How do I add card?
Go to your Atome app:
1) Go to "Me" and then click "Payment method"
2) Click on the card that you wish to set as default card
3) Use the toggle to set the card as default. Toggle switches are grey (when off) and green (when on).
Please note that every account will require a card tagged "default" and all the payments will be deducted from the card by default.