I want to reset the balance in the app store

If you are trying to zero your balance and still have a valid credit or debit card, 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.

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

If you choose this option, use the direct link I just provided. You can use the general support link at Official Apple Support but it will just eventually lead you to the link above after you spend several minutes exploring the support web site. I’m just saving you some time and effort finding that link. ;-)

Alternatively give Apple a call:

Contact Apple for support and service - Apple Support

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

Change your Apple ID country or region - Apple Support

You’ll either need to spend it or if it’s not enough to purchase a product or service, you’ll need to contact Apple Support to have your account set to zero. If you’re in the US please call 1-800-MY-APPLE or outside the US, consult the support article below.

Contact Apple for support and service - Apple Support

Change your Apple ID country or region - Apple Support