According to the NCL website:
Guests who had an active reservation on a suspended cruise in May 2021 will automatically receive a refund of their cruise fare in the original form of payment for the amount paid by March 23, 2021. Additionally, a 10% off coupon will be automatically added to the guest’s account, if the guest has not already received one for a previously cancelled sailing. The 10% FCC coupon is valid for one year from date of issue, and can be used for any Norwegian Cruise Line voyage embarking through 2022 and is combinable with any other Future Cruise Credits and all future promotions at time of booking.