I think you are thinking of TOGGLE HEAD TRACKING and it currently unbound so you need to bind a key to it however when turning TOGGLE HEAD TRACKING off it resets the view to looking straight forward so I’ve written a workaround that you can use here(it will keep your view where you are currently looking at): https://forums.flightsimulator.com/t/making-tobii-eye-tracker-work-with-su8/472111/252.
F12 is the new hidden function to Center/Reset your tracker.