Please contact the official Apple Support about that, only they can clear your Apple Account balance.
You can use this link to do so:
Contact Apple Support
If you can not contact them, you can spend the remaining balance to buy an app or content from Apple, which costs slightly more than the remaining Apple Account balance, so that your secondary payment method will be used to charge you for the rest of the payment.
If you haven't already, take a look at this article, to make sure you have completed all steps to be able to change the region successfully:
Change your Apple Account country or region - Apple Support