I would windows key to launcher, start typing "optimus manager", and click it or press enter, how you launch apps. I could also use terminal. Same result: nothing.
I got around it by installing the gnome extension widget, but I was never able to open the optimus-manager settings app.
I uninstalled optimus and went back to bb so I could deactivate nvidia, as it's not disableable (in optimus) on lots of Dells, mine included.
I was really in intel mode, and nvidia was really on. It approximately doubles the power draw, and doesn't show up in powertop, so it's painfully easy to see: total normal idle draw is around 8-11W, depending on how idle my idle is, and in Optimus Intel mode, it would never draw below 18W, because the Nvidia chip is sucking another ~10W constantly. No processes in powertop account for the ~10W. It's just the Nvidia package sucking power for nothing.