How do I clear my Apple Account balance to change region/country?

You can contact Apple directly and they can clear the balance:

Contact Apple for support and service - Apple Support

Also review the other steps you may need to take including:

• Cancelling subscriptions. Cancelling just prevents them from being renewed and they will still remain active until the expiration date. If you want to remove them before that time, you will also need to have Apple do that.
• You may need to add a payment method that is in your new region if you want to use that App Store. The region of your payment method is how Apple determines if you are using the correct App Store and it must match the region on your device.

Change your Apple Account country or region - Apple Support