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

Buy something more expensive than your balance and use a different payment method from the current region for the extra amount; if you can't, click here and ask the iTunes Store staff to zero it.

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After you do that, follow the steps in this Support Article for additional steps you may need to take, such as:

• Remove all subscriptions. Cancelling a subscription, just prevents it from being renewed, but will remain active until it has expired. To remove it immediately, you may need to contact Apple after cancelling.
• You may need to add a payment method for your new region if you want to use that App Store.

Change your Apple Account country or region - Apple Support