To delete a single registrant from an event:
 
  1. Navigate to onBoard > Settings
  2. Select Event Registration
  3. Next to the Event Registration, click Edit
  4. Under Edit Registration, click Registries
  5. Filter Status to All
  6. Click View
  7. Under Registrant Name, click the user's name to be removed
  8. Under Delete, click Delete Registrant
  9. Click OK in the confirmation box