
Hit "change store", and you should be able to access it. It will tell you that the app is only available in Australia.
Click here to go to directly to Animal Crossing: Pocket Camp's App Store page. Make sure when you put in an email that it's one you own and can access, so you can actually use the Apple ID! Create a new one, and set your location to Australia. It'll prompt you to sign in to your Apple ID or create a new one.
Go to the App Store and try to download a random app. The next screen should show your Apple ID at the top, and tapping on it should allow you to sign out. Log out of your Apple ID on your phone by going to Settings, tapping on your name, and then "iTunes and App Store".
Otherwise, there's nothing illegal about this process! On iOS
Keep in mind, if you download the Australian version of the game and later decide to play it when it comes out in your region at the end of November, none of your save data will transfer over.