how to remove my credit balance, so that i can change my country

Any credit balance must be spent before changing your country.

If you do not have a credit card to buy something, contact iTunes Store support for assistance:

Contact iTunes Store support

More information:

If you can’t change your iTunes Store country or region - Apple Support

Thanks

So, as written in this support article, contact Apple Support using the link that you find at the bottom of the article itself:--> Change your Apple ID country or region - Apple Support

Extracted paragraph:

If you can't complete any of the steps, can't change your country or region, or you have less store credit than the cost of a single item, contact Apple Support.

Regards

GIulio