The video is very old and outdated. The toggle you see for Plex is not for enabling the service itself, but was for allowing public access without login. This feature has since been removed. Other services like, Deluge, CouchPotato, Sonaar, Jackett, SickRage, Rapidleech etc etc. Do show in that service field. Plex is a media service and thus has no entry on the list. If you see your Plex link in the menu, then the service is active.
We may build in the option to restart, or turn the service on/off, but at this moment there is no real need.
Also, take note that services do not show up in your service controllers unless they are installed.