Unfortunately, you cannot transfer Walt Disney World or Disneyland tickets to someone else once you’ve used the ticket for admission. For example, one guest cannot purchase a multi-day theme park ticket and then transfer it to another guest after the first use.
Fortunately, if you have not yet used the ticket it can be transferred to another guest.
Paperless tickets can be reassigned within the My Disney Experience app to someone on your "Family & Friends" list if they have not yet been used. Go to the "My Reservations" section of the app, choose the ticket you want to change, and click the "Reassign Ticket" link next to it.