You can edit a contact's information by clicking on the existing contact's name directly from the reservation page OR by searching in the "Customers" section located on the left hand navigation bar. Once you have opened the contact you will be brought to the boaters profile page. There you can view that boaters reservations at your marina, and the boats and credit cards listed on their account.
On the "Boats" and "Credit Card" pages, you can add new boats and credit cards to the boater profile for future reservations. From this page, you also have to ability to create a new reservation for this boater by selecting "New Reservation" on the top right of the boater profile page.
If a boater is without internet, or otherwise unable to access Dockwa and update their credit card - this is a good opportunity to get their card information and enter it into their contact profile in your Dockwa account to ensure payment. Once you have done this, you will also need to Manually Re-run their Payment if their card previously failed on their reservation.