how to reach zero on my apple id balance

Here are two ways you can remove all your Apple ID balance:

Spend it:

If your store credit is less than the cost of a single item on the iTunes Store, App Store, or iBooks Store, you can add a payment method such as a credit or debit card to your account [ how to add a card --> https://support.apple.com/HT201266 ]. When you buy an item, you will use the remaining store credit and the rest will be charged to your card. This payment method has to be from your old country.

Have Apple keep it

"If you still can't change your country or region, or you have less store credit than the cost of a single item, contact Apple Support." Apple will remove the balance and keep it.

Click here --> https://support.apple.com/choose-country-region/media-services Select an option and keep on working your way down the menu until you get to one saying your "topic isn't listed". This will present you with support by chat or telephone call.

Or call Apple Support --> https://support.apple.com/HT201232

References:

Click on this link to read full information about requirements for changing store country:

Change your Apple ID country or region --> https://support.apple.com/HT204447

https://support.apple.com/HT202359 --> "Before you can delete your Apple ID or change your Apple ID country or region, you must spend all of your Apple ID balance. You might also have to wait for any pending refunds to process."