You can, you just have to open a ticket for it. Support-->Create a New Ticket-->Request New Winner-->search for this GA-->select pio--> previously won the game or already in the account. Then just write to the free text box that "He asked and agreed on the reroll as you can see in the comments" or something like that. I've already did that many times when my giveaways ended up the same way. Sadly the checking logic is not perfect especially in case of bundles. Again, sorry for the caused trouble.