The winner of my giveaway already has the game

You can request a new winner.

Just wait, support is slow.

Winner may have base game, but not dlc.

Have you already sent the key?

Open a support ticket asking for a re-roll. Wait for at least a week to get an answer. Your newly assigned winner might have the game too -> rinse and repeat.

Since the winner said they already own the game and asked you to request a new winner, just go to the Winners page and click the text next to the winners name that says "Request New Winner". Fill out the support ticket and wait a few days for support to pick a new winner. If you already did this, then just wait.

Normally users will not be allowed to enter for a giveaway if they already own the game, but the version you are giving away comes with DLC. This causes an issue where the site cannot detect what users own the DLC and it will let everyone enter, even if they already own the game. Users that don't know what games they own or don't pay attention to what giveaways they are entering might enter the giveaway even though they already own the game and the DLC, so you may have to reroll a few times before you get someone that doesn't already own it.

It can take a few days or maybe a week for support to process the ticket and select a new winner depending on how busy they are.