Winner owns one of the games in the bundle

reroll

I personally would reroll but that's up to you I guess.

If you asked people not to enter if they own any, just go ahead and ask for a reroll.

I would request a reroll

You can get a re-roll if the giveaway winner already owns any part of the giveaway, so I suggest doing that. :) And maybe ask the winner to try reading next time... :)

You can request a re-roll

You can ask a reroll. It's up to you.

It's up to you. You can submit a reroll request or give the gift, but I'd say owning half or more of the bundle is perfectly good reason to reroll, especially if you explicitly state that people should not enter if they own one of the games. Here's the relevant rule from the guidelines:

Try to refrain from entering giveaways for packs if you already own the majority of the games contained within. The giveaway creator may request a new winner if you own a high percentage of the packaged games.