Carfully slide the larger part of the rubber boot forward, you will see the edge of the pushrod has "flats".
Hold the flats with a wrench, and break the jam nut loose, then you can turn the rod in or out until you get the position you want with enough play, so the switch actuates when you desire.
You can also disconnect the rod end side (eyelet) and hold the rod and adjust the rod end (does the same thing).
If you pull the connector off the swotch, you can use a light or meter to signal when the adjustment is where you want it, rather than trying to listen for the solenoid to click.