How do you Debug iOS App Game Center Integration?

Hi

App is published on the Apple App Store however the leaderboard doesnt work. I had the same problem for android but I was able to easily debug it and fix the problem within an hour. However I can't even work out how to do the same with this.

I know iTunes connect is a bit funny with testing Games Center in its Test Flight beta program, which just makes the problem harder for me.

I cant find anything online, I dont know how to debug an app in Xcode, I dont even know if I can debug my Game Center integration code properly if game center only works under certain enviroments.

Can anyone help out at all please or does anyone specifically know how to test game center?

Cheers people