The lever will release to the open position and move from the centre back to there. You need to click it over to the propedal position for it to stay there.
So just pust it to the centre and let go, that's the open position.
The shocks have an underlying propedal platform dialed in and the lever simply increases the amount of platform (low speed compression) if the shock is tuned for a particularly active suspension design, the underlying propedal platform might be quite firm and you won't feel much difference when the lever is in the on position, but there will be a subtle difference.