Winner owns Game already

1. You can't (unless it wasn't actually the key but a HB link), you'll have to trust the winner to tell you the truth.
2. You have to "request another winner" (or was it a new winner?) and support has to approve the reroll.

If winner says he didn't use the key, why not give it to the new winner? Add the new winner too. Worst case, it's a dupe, so he'll tell you.
And you can request new winner any time. (Example)

Ok so i just have to trust the winner. and if the key is already used i have to get a new one. we will see

have same problem. winner confirm if already owned game after a week and ask for reroll . im not gonna risk doing reroll and let him own it.

He wouldnt tell you to reroll if he used key :) If he did , report him to sg and delete ga if you dont have spare key, ofc with informing admins before you delete