If you signed up with an account (using an email and password), log in and click the title of the sign up under the section for 'Items I've signed up for' to quickly view the option to edit/swap/or delete your sign up.
If you signed up without an account, you can go back to the sign up by following the link that was provided in your original invite or you can go back to the confirmation email that was sent to you after you signed up. When you view the sign up, you'll see a link at the top that states,"Already signed up? You can change your sign up." Click that link to follow the steps to edit yoursign up slot.
If you still cannot locate the sign up, contact the creator of the sign up. Click to view the sign up
and from the general sign up information, next to the “Created by” text, click the envelope icon
to send an email to the sign up creator.