Hi
Any credit balance must be spent before you can change your iTunes Store country.
Apple advises that, if your credit balance is less than the cost of an item on the iTunes Store (including App Store), then you can add a credit card to your account. When buying an item, your remaining store credit will be used up, with the remainder of the purchase price charged to your credit card.
If you do not have a credit card or need further assistance, then contact iTunes Store support for assistance:
More information and instructions:
If you can’t change your iTunes Store country or region - Apple Support
(Note that you are not talking to Apple here - this is a user-based technical support community).