Thanks.
I'm new to this site and accepted this without realizing I had it already (I thought it wouldn't show up on the giveaway page if I had it, but apparently that doesn't work with DLCs).

I contacted the site and they told me to "Comment in giveaway page asking to reroll, so the creator will get a notification.", so you can give it away again.
Of course, I already marked it as received so I don't know if causes a problem (they said not to mark it as received, but I'd already done that).