If you're looking to update your billing method for your Persist subscription, log into the My Account page and find the Subscriptions section on the left-hand side. Once you are there, you can update your billing information by:
Click on current Subscription
Click on "Edit Payment Method"
Send Email
Check email and follow prompts to change Billing Address and Payment Method
If you are looking to save your billing information for a faster checkout of ebook or apparel purchases, go to My Account and find the "Payment Methods" tab to log your preferred payment method.
If your subscription is via ATOM please reach out to support@trainatom.com, they will be able to assist you with any subscription changes.