How attenders can delete their own response

Have the attender bring up their confirmation email

When initially filling in the form, the attender will have been sent a confirmation email. Have them bring that up. It should look something like this.

Click the cancel button

Ask the attender to click the "Cancel Registration" button. When they do, they'll be prompted to confirm they meant to cancel. After cancelling, they will no longer be listed on the results and the number of attenders count will change accordingly.