To add/update your payment method in the Atome app:
1) Go to "Me" and then click "Payment method"
2) Click "Add a new card"
3) Complete the card details required to process payment transactions and click "Save"
Do note that all the payments will be deducted from the card tagged "Primary" by default. If you have ongoing orders, you will not be able to delete this card unless you have added another card and set the latter as "Primary". There needs to have at least one card to be in your active account to deduct the outstanding bills.