Inform the front desk at check-in about the credit amount. The CM (who won't be able to view the credit on their screen) will get the manager to verify the credit and it will then be applied to your room folio. Use your magic bands during the trip and it will gradually just use up the credit. You can request a copy of your folio anytime during the trip to see your remaining balance and current charges (I obtained of copy of mine daily). Any credit remaining at check out will be credited to the credit card you left on file with the front desk. FWIW, I never received any confirmation email documenting my credit, so I certainly would not have had that to show the front desk anyway.
