To change your Statue City Cruises reservation, please click the manage booking link from your Statue City Cruises confirmation email or go to https://www.statuecruises.com/ and click the manage booking button found under Manage Booking -> Change Tour Date on their website.
Enter your confirmation number found in your confirmation email and email address. Once you enter your confirmation number you are attempting to change, there is Refund terminology used on their site. Once you proceed with the 'refund' (even though this just means your reservation is cancelled) you can then make a new reservation.
Note: You will receive a confirmation number (order) and email for each individual CityPASS ticket regardless of whether all tickets are in the same CityPASS order. You need to manage booking for each individual ticket.