Step 1 - Go to your form 'Dashboard'

Step 2 - Click ‘Number of Responses’  

Step 3 - In the list of responses, find the registration that needs canceled and click ‘Details’

Step 4 – Click ‘Cancel Registration’

A cancelled registration will still show in ‘Number Of Responses’ and in reports, and can be re-registered by an administrator. If your event has a max capacity, canceling a registration will make it so the response does not count against the capacity.