I had a similar problem but managed to sort it out! I first changed the region online by logging to appleid page but that still didn’t let me change my billing address in the phone settings. The next thing I did was going to App Store and changing my region and billing address there. That automatically changed it on iTunes and in the settings as well. It seems like there’s an error where instead of directing you to the App Store, it takes you to iTunes. It’s impossible to change the region from there, hence why it shows the missing data info. Hope that helps!