The OwnerUrn parameter specifies that you want only contacts for the Response Group application. The Filter parameter is an LDAP filter that will select only contact objects that have been at some point tied to a Response Group workflow, and unselect the two contact objects (Presence Watcher and Announcement Service) that are automatically created with Response Group application. The RegistrarPool parameter allows you to select only contacts associated with a specific pool.
5. The preceding command should output all the properties of every contact object formerly associated with a Response Group workflow on the specified pool. If you are satisfied with that list, you can delete those contact objects by simply re-running the same command and adding the Delete parameter at the end, like this: