I need help to empty App Store credit

Hi! You can purchase anything from the App Store and it will deduct from your balance. If the cost is more than what's in your balance, the remaining amount will be paid using the payment method associated with your Apple ID.

If you don't want to do this, I'm pretty sure Apple Support can clear your balance for you if you contact them directly: https://getsupport.apple.com

Have a great day!