Sadly there isn't much you can do except ask to return it and buy another model (or a refurbished/owner by a third party Pre-2018 MacBook Air). If you can't return it due to be over the limit of days possible, the best you can do is call AppleCare, get escalated to a senior advisor and convince them to send you a Webcam for free due to the Macbook's Air info page obviously false advertising:
"The FaceTime camera lets one — or many — of your friends and family members see you in high definition."
Source: https://www.apple.com/macbook-air/
IF you need a good camera for work (and you bought it for that reason), and the info page states it give you "high definition" camera, then I feel most agents would agree with you deserving a free webcam if it cant be returned anymore.