Trouble creating a giveaway

Hi,

I am very new here. I am trying to create a giveaway for Batman: Arkham Origins - New Millennium Skins Pack which I got from the WB Humble Bundle. I see a few of these (as giveaways).

However, when I try to do it, I don't find it as an option under the first dropdown (Select a Gift).

I see Batman: Arkham Origins and then Batman: Arkham Origins Season Pass.

Should I be looking elsewhere?

Thanks