Not sure about FAA number, as I'm from Canada, but you can contact DJI with the serial number, and they can reach out to the pilot and notify them, in order to put them in touch with you. There are several methods to contact DJI, I'm not sure specifically which ones worked for people in the past (I know this has been done a few times before, and the drone has been returned). I'd start with the live pre-sales chat on their website, and see where they direct you to. They likely aren't the right contact, but hopefully they can put you in touch with the one who is.