I need help to empty my AppStore balance

Contact Apple directly and they will assist in clearing your balance.

Contact Apple for support and service - Apple Support

If you have less store credit than the cost of a single item, contact Apple Support. You can also purchase something for more than your balance and the remainder will be billed to your payment method on file.

For step-by-step instructions on changing your Apple Account region 

⇢ Change your Apple Account country or region - Apple Support

Hello! Thank you for using Apple Support Community.

I see you want to empty your account balance. You can use one of the methods below:

1) If you are trying to zero your balance and still have a valid credit or debit card from your original country, you may purchase an item from the App or iTunes Stores for more than your balance. The remainder will be billed to your card, leaving you with nothing in your account balance. This is the easiest solution (you can do it yourself!), plus you get to use your money for something for yourself instead of donating it to Apple.

2) Alternatively, you could ask Apple Support to remove and keep the balance. Remember that the people on this forum are just other Apple products users like yourself and are unable to do this for you. Use this link Apple provides to take you directly to the managing and editing an Apple ID people who will do this for you --> https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0998&symptom_id=20198

This is more direct than using Official Apple Support which will just eventually lead you to the same place after some searching.

If the above direct link does not work for you, go to https://getsupport.apple.com/?s=n , enter “empty balance” or “zero balance” in the search line, press enter to search, then on the next page select “Clear Apple ID balance”. On the next page select a chat or telephone call option.

Alternatively give Apple a phone call. Find a list of telephone numbers at: Contact Apple for support and service - Apple Support

When asking about this because you are changing regions, take a look at this article:

Change your Apple Account country or region - Apple Support

Have a great day!

P.S. The general support link at Official Apple Support takes you to the top level of the help search menu from which you then have to do additional searching. The direct contact links I provide are the ones that Apple provides specifically for people wanting to ask them to remove balance.