I don't know if it's the same for the Trooper. But on my 93 Rodeo, I had a real difficult time. Until I found an open slot in the plastic under the steering column. In the Rodeo, you have to get a long screw driver and go up from underneath the dash.

I hope this gets you started in the right direction. I nearly tore my dash off trying to figure out how to get behind the cluster, just to reset the O2 sensor.

Good luck
-Robert