Hi Karen, welcome to planDisney!
While
theme park ticket purchases are nonrefundable and nontransferable per
Disney's eTicket Terms & Conditions, I do have good news! You can certainly book a
theme park reservation for another day that has availability. I suggest monitoring the
Theme Park Reservation Availability Calendar as this will allow you to see park reservation availability.
I'm happy to walk you through the steps of booking a reservation. First, you need to add your tickets to your Disneyland Resort account. I always found this to be the easiest through the
Disneyland Mobile App. Once you download the Mobile App, open it up, click the three horizontal lines in the bottom right-hand corner, select "Tickets and Passes", and then select "Link Tickets & Passes". Next, you scan the barcode of your ticket that you would like to link. Once your ticket is linked, head on over to the Disneyland Resort website, select the "My Disneyland" link, click the "Ticket and Reservation Details" link, and then select "Make Park Reservations".
If you have any more questions, please do visit us again!
See ya real soon!
Jin