Once you have set up your client's payment schedule, you may need to update the credit card/ACH on file.
To update the payment method, go to your case in Payments > Payments and click on More Actions.
Then click Update Payment Method.
You can then select if you want to update the method for this payment only, or all future payments on the schedule.
Next, select the Payment type (Credit Card or ACH). And set up the payment method.