How to change App Store's country after cancelling Apple Music subscription?

There are several things you must do before changing the country on your Apple Account. They include:

• 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.
• Make sure that you have a 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.

For more details, try this:

Change your Apple Account country or region - Apple Support

Cancelling a subscription just prevents it from being renewed and the service is still in effect on your account until the end date. If you want to remove the subscription early, you will need to contact Apple directly and that will need to be done if you are looking to change regions.

Contact Apple Support - Apple Support

Also be prepared to add a payment method based in your new region if you want to use the App Store after the change.