You can update your payment method through your Rythm account.
How to add or update a card
Log in to your Rythm account.
Go to Account → Billing.
Select Manage Payment.
Add a new card or update your existing payment details.
Rythm uses Stripe to securely process payments and help you manage your saved payment information.
Update your payment method as soon as possible if your card has expired, been replaced, is no longer active, or does not have sufficient funds. Your payment must be successful before Rythm can process or ship your next test.