You can ask Support to zero balance your account.
World-wide Apple Support -
https://support.apple.com/en-us/HT204169
Support by phone, email or chat -
https://getsupport.apple.com/
Apple Support by Twitter -
https://twitter.com/AppleSupport
iTunes Support -
https://support.apple.com/en-euro/itunes-contact
You cannot change your account to a country in which you are not a legal resident. Aside from being a legal resident of China, you would need to provide an acceptable payment method from China with a verifiable Chinese billing address.
And should you persist in doing so, you may find that your iPhone is locked to that country for the next 90 days.
ASC - Late 2012 Mac mini, macOS 10.15.5; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.5.1; iPhone 8+, iOS 13.5.1; TV 4th Gen, tvOS 13.4.6; HomePods, audioOS 13.4.6 and Airport Express w/ Airplay 2