I've got you covered in updating your billing information via QuickBooks Online.
Payment information updates must be done using QuickBooks Online in a web browser.
Go to Settings ⚙ and select Account and Settings.
Select Billing and Subscriptions.
Select Edit ✎ next to Payment Method.
Enter the complete credit card info and verify the billing address in QuickBooks Online is the same as the one shown on your credit card statement.
Select Confirm card.
Select Save Changes.
Once done and you're still getting credit card expiration notices, I'd suggest getting in touch with our QuickBooks Online Support. Agents can take a look at your account in a secure environment and synchronize the new credit card information in the system.