If you need to update your card on file, this can be done using the app as long as you are logged into your account. You will first want to navigate to the Payment Method page:
1) First select Profile from the menu options at the bottom of the app screen (Home, Chats & Profile will be the listed options)
2) On the Profile page, you will see a Payment Method option - select this to go to the Payment Method page.
Once you are on that page, you will see an option to Add New Card, and can fill out your card information once this is selected.
After you've completed and submitted your new payment information, the new card you entered will automatically become the default payment method for your account. If you go back to the Payment Method page, you should now be able to choose your desired payment method, and change to any other cards on file if you'd like (the default will have a blue check-mark to the right - see below).
If you'd like to delete an unused card from file, you can also select the "Edit" button at the top right corner. This will reveal a red icon next to any card not currently set as default, and you can click that icon to remove a card from your account.
You will not be able to remove the default card, so if for any reason you need to remove all payment methods from your account, please contact customer support at firstname.lastname@example.org and we can assist you with this directly.