We flew home yesterday so I can speak to this.
While we were on the island, I received an email from American Airlines encouraging me to download the Verifly app in order to complete the new requirements to re-enter the USA. To be honest, the app itself presented a few problems for us (more on that later) but it did give me the opportunity to complete the attestation form online before departing.
Yesterday morning when we checked in at SBC, they presented us with the attestation form and told us that we needed to complete it and present it when we checked in for our flight in Saint Maarten. When we got to the AA checkin desk in Saint Maarten, they also presented us with the form and asked us to fill it out and seemed surprised that we already had one completed. In any case, it is a simple matter to check the proper box and sign and date it there at the check in desk.