The camera is facing straight up. The sensor can be seen and the connector is pointing up towards the tach. I can't see how to access it save possibly pulling the screw on the side and maybe pulling the sensor down...
don't know how the hell you'd get it back in there. Looks like you have to pull the dash pad and that's insanity.

 

Only reasonable approach might be to remove the switch in order to add the harness adapter then reinstall sensor.
I cannot fit in there to do it.
My daughter is now giving it a shot.

 

This reminds me of my V1 nightmare. I was replacing the clutch and one of the tips that I read was to use the slave cylinder to help push back the trans. Once the bell bolts were removed, I hammered the clutch pedal with my foot. I immediately felt the pedal fall and heard parts scatter.

It turns out that I had disconnected the slave hydraulics and when I reconnected, didn't get the coupler fully engaged.

So, I had given a full force boot to a clutch with nowhere for the fluid to go and the weak point is that little plastic rod end that connects the master to the pedal. Replacing the master is about as fun as accessing that sensor...

Good luck my friend.

 

Success! My daughter, with her smaller, more dexterous hands along with her ability to contort her body to get her face under the dash at the same time as her hands meant that she was able to get it done.
The access there is so tight that even after getting the switch out, it's still not a cakewalk as there's no room for the pigtail's added length to fit into the spot(!)
From the pics I've seen, the Camaro and Corvette applications have the switch mounted such that the plug is easily accessible. Cadillac, though, needed to be exclusive. She DID get it done, though.
It took an hour-fifteen to do what would be a five-minute job in other cars. Such has been the story of this whole adventure!
if you are going to tackle this, know that you really need a box end ratchet wrench in 7mm. I have multiple drawers of metric ratchet wrenches from six to thirty-two... no sevens.