Simple, log in to Amex account, go to offers, view all, find NCL offer, add offer to Amex card.
When you spend $1000 on NCL.com or via telephone using that card, you get a $350 credit. You had to add the offer to Amex card before Oct 14 or 18 (forgot exact date). And you have till Dec 31, 2022 to redeem the offer.