Can I reset my Game Center achievement/game progress ? Can Apple support help me to do so ?
As title said
The only way is to delete the app itself. It will then ask if you want to also remove the app from gamecenter. Select 'remove'. If you deleted the app but didn't select remove. You can go to gamecenter, find the app and swipe it to the left. It will say delete and you can delete it from there.