How can I clear my Apple Account balance to change region?

Contact Official Apple Support and request.

You might also refer to this article for additional requirements:

Change your Apple Account country or region - Apple Support

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~

Thank you for reaching out. 🤗

There are many parameters that need to be taken before changing regions because currency valuation is not the same across various regions.

If you are changing regions:

• Spend any balance remaining on your Apple Account. If you’re not sure whether or not you have a balance, check your Apple Account balance.
• Cancel any subscriptions that block a country or region change and wait until the end of the subscription period. 
• Wait for any memberships, pre-orders, movie rentals or Season Passes to complete and wait for any pending store credit refunds to process. You can cancel a pre-order.
• You may be required to enter a valid payment method for your new country or region. See what payment methods you can use.
• Redownload your apps, music, movies, TV shows and books on any devices that you might use to play or read them in the future. Some types of content might not be available in your new country or region. Learn what types of content and services are available in your new country or region.
• After you update your Apple Account billing address and payment method, you can upgrade your iCloud+ plan using the pricing in your new country or region.
• If you need to empty your balance, Contact Apple Support to request a reset of your account balance to zero.

For full details, learn how to → Change Regions for step-by-step instructions.

Good luck! 👋🏼😉

Smiliñ 😎 Brian