To add a booster pack to the draft, first pass the booster pack that contained Lore Seeker to the next player. Then open the new booster pack, draft a card, and pass the new booster pack in the same direction. Then you'll receive the booster pack you would've received had you not added a booster pack, and the draft round will continue. The added booster pack will last a few picks longer than the rest of the booster packs opened that draft round.