I’d like my credit balance to get 0$

In the interest of full disclosure here are two additional methods to remove account balance. Since Apple does not include them in the support article Change your Apple ID country or region - Apple Support I am posting them separately.

+ "Spend any balance remaining on your Apple ID"

If you find your store credit is less than the cost of a single item and you still have a valid payment method for your old country such as a credit card, you can use the payment method to make up the difference in the cost of an item ( How apps, content, and subscriptions from Apple are billed - Apple Support ). Perhaps buy something such as a music track which you can download and also keep a backup copy. Remember that anything purchased may not be available for re-download in another country but as long as you have your own copy you will always have it.

This method --where you get to use your balance by spending it instead of giving it to Apple-- used to be in Apple's support article about changing countries, but a few years ago Apple stopped mentioning it even though it is still perfectly effective.

+ "Check your Apple Account balance" refers you to Check your Apple Account balance - Apple Support

Note the sections "If you have an Apple Account balance that you can't use", and "If you plan to delete your Apple ID or change your country or region" Again it is valid and is even in Apple's documentation. However, since it only works in very limited situations, it may be this is way it is not really recognized by Apple as a practical way for removing account balance though theoretically it may work for some users (I have never seen anybody say they have used this method).

Hello,

I see you have remaining balance that you wish to remove from your Apple Account. In Apple's support article Change your Apple ID country or region - Apple Support Apple lists only a single way to do this:

"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 offers this specific link for that service --> https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0998&symptom_id=20198

Apple will remove the balance and keep it.

Hello ~If you are trying to zero your balance before changing regions…you may purchase an item from the App Store for more than your balance and the remainder will be billed to your credit card on file thus zeroing your balance . You may also go to lower left hand corner and click on Support and they can zero it for you or:

Contact Apple for support and service

Also if you are changing regions take a look through this article as well:

Change your Apple ID country or region - Apple Support

~Katana-San~