On the left side of the main menu, click on ORDER OVERVIEW.
Search for the order whose customer data you want to modify.
Open the order by clicking on the order ID.
Click on TICKETS in the right menu.
Now click on the grey CALENDAR of the ticket where you want to change the date.
Choose another date and click on SAVE.
Tip: When you have changed the date and time of the order you have to generate the tickets again and then send the confirmation email again. That way the customer will receive the tickets again with the new day and time slot.