It states on the website under the quest card:
Free first and second checked bags – a savings of up to $320 per roundtrip
The primary Cardmember and one companion traveling on the same reservation will each receive their first and second standard checked bags free (up to $35 value for the first checked bag and up to $45 value for the second checked bag, each way, per person) on United-operated flights when the primary Cardmember includes their United MileagePlus® number in their reservation and purchases their tickets from United with their card.* Same page link to Offer Details For complete details, please visit united.com/ChaseBag Opens Overlay .