For fixing
Its coming bad message 400 when try to change my country and region
Its coming bad message 400 when try to change my country and region
Before you update your location, you must spend your store credit, cancel your subscriptions, and get a payment method for your new country or region.
What to do before you change your country or region

Before you update your location, you must spend your store credit, cancel your subscriptions, and get a payment method for your new country or region.
What to do before you change your country or region

It would be better if you can please re-post with a screenshot, in order to understand the phenomenon better. Images/pictures speak louder than words. Do not provide any personal credentials, such as email id, apple id, IMEI number, Serial Number, Phone number, Order ID, if you are sharing a map ensure your location is not identifiable. Etc.
For fixing