You can return your tickets by logging in to your OutSavvy account and cancel the tickets on the My Tickets page. If you are able to cancel your free tickets you will see a Cancel Order button on that page.
You can also cancel free tickets on the app on the ticket confirmation screen.
If you checked out as a guest, you can click on the My Tickets link in the confirmation email. If you are able to cancel your free tickets you will see a Cancel Order button on that page.