Had this on my '93 Trooper as well.
You are right about the screw behind the instrument cluster (I learned the
hard way... called the 3 dealers, none claimed to know how to reset it one
said something about inside the instrument cluster... I took the cluster
apart which was a big mistake. $600 later to replace the cluster because
my speedometer no longer worked.) The key is to not take the instrument
cluster apart once you have it out of the vehicle and you will be fine.
Once you pull the cluster out (it is all electronic so no spedo cable to
worry about) look at the back... in about the middle, you will see a screw
(don't remember what it says on the circuit board, but there is a position
you can move it to right next to it, and I think it is under a piece of
tape. But it is the only other place for you to put the screw that is
remotely close to it.