Only the lead booker is able to reclaim a ticket previously shared to another person.

To do this, log in to your order here and click 'Manage/Assign Tickets to attendee'

Next to each entry ticket previously shared, you will see the option to 'Reclaim' the ticket.

If selected the original attendee will receive a notification to confirm the ticket has been recalled and you will then be able to re-assign or claim the ticket as you wish.