Hello there, j-knoll.
Good to see you here in the QuickBooks Community. Let me help walk you through on how to update your payment method in QuickBooks Online (QBO).
To do this, here's how:
For additional reference, you can check this article on how to update your credit card information.
This will get you on the right track. Feel me in if you have additional concerns about updating payment method. I'll be around to help. Have a good day.