I'm not an Apple user, so I can't offer much help.
But if you could go to the download centre and see Fly listed, this is what it would look like:
Click on it to make it larger if needed.
I wonder if you scanned the QR code, would that work?
And...
1. The app you want is DJI Fly
Go Fly is a fake app and should be avoided.
2. Have you tried installing the app that DJI say only supports phones?
Even though DJI say that, it's just not true.