Hi Scott. I'll be happy to give you the step by step on this procedure.
First, as noted elsewhere, the reset is actually two pieces. One is the square button you see on the outside. The other is an L-shaped part inside. Look at your button. If there is a small, black, plastic dowel broken off in the back of your button, you'll need both parts to get it working again.

Now then: Do you know how to remove the instrument cluster?
1. Remove headlight switch knob and dimmer knob.
2. Center your steering wheel
3. Pop out the headlight panel with a small screwdriver
4. disconnect rear fog light switch (if installed) by unplugging
5. Remove both square accessory guage panels to the right of inst. cluster
6. Remove four screws, two on each side of the inst. cluster (phillips)
7. Remove the headlight switch panel support (black metal bracket)
8. Pull the instrument cluster out on top of your steering column cover
9. Reach in back from the right side and disconnect:
A. Large, round, multi-pin connector-wiggle it out carefully
B. Small, crescent-moon multi-pin connector-usually easy
C. Overdrive lite spade terminal, lower right hand of inst. clust. rear
D. Cruise control speed signal-female spade connector near speedo rear
(if you have cruise. Look for the double male spade terms near the
speedo back)
10. Disconnect speedo plug. If original, it may have a plastic bracket over
the plug that holds it to the back of the speedo--save it if you can!
11. Do you have a tach and small clock? If so, remove black plug from back
top of the tach.
12. Remove the inst. cluster by sliding to the right.
13. There are 8 or 10 phillips head screws all around the perimeter of the
rear panel of the instrument cluster. Remove them all. Some go through
the back of the tach/clock, which ever you have installed.
14. Remove the entire back of the cluster with all instruments.
15. Look on the bottom of the speed. You will see a small metal crossbar
below the face. The L-shaped activator lever "clips" to this bar.
Pushing on the button pushes the activator lever, which moves the bar
back, resetting the odometer. If the lever does not have the black dowel
on it, it is broken off and the lever needs to be replaced.
16. If you can get the dowel out of your button, or if it is loose in the
cluster, do not attempt repair by gluing it to the lever, it won't last.
Replace the lever. Junkyard??
17. While you are in there, service the temp guage compensator board.
18. Look below the temp/fuel guages. See that little circuit board? Unclip it
and remove it. It sits on four little contact pins. Clean the contact
pins and the receptacles and put the board back into it's guides. Make
sure to slide it all the way "home".
19. Great time to check all the warning light bulbs and clean out the cluster!
20. Carefully guide the instrument panel back into the cluster housing. You
must make certain the odometer button does not hang up on the way through
the clear front window. No other tricks here. Reassembly is the reverse of
disassembly...as they always say, with the following cautions:
A. If you do not have a tach, the white/red female spade terminal wire
behind the cluster should NOT be connected to anything! If you plug it
into the cluster, you can fry the speedo or other components.
B. Blue wire with spade, if there is one, is for the upshift indicator--if
you don't have a stick, relax. If you do, that and any cruise control
connectors are the ones that go on the double male spade lug next to
the back of the speedo (passenger side of speedo). Connect the cruise
lead if you have cruise, and the upshift indicator if you like big
brother telling you when to shift--and if you have a stick.
C. The overdrive (automatic gearbox) upshift indicator is the lead
with the tiny female spade that plugs onto the single tiny male spade
lug on the very bottom right corner
D. Be careful plugging in both the multi-pin connectors. Align the center
lug and pins carefully. Make sure none of the wires "back out" of their
plugs. When they are loose, sometimes this happens.
E. Plug in the speedo with care. The circuit board has been back there
baking in the dashboard for years, it's brittle. Replace clip if pos.
21. As you replace the cluster, remember you need to navigate it over the
bottom edge of the instrument panel frame and under the top--at the same
time.
22. Don't forget to put the metal bracket in place on the left side before you
put the screws back. Replace knobs and right side blank panels.

Atsa wrap! Don't hesitate to e-mail with any questions: dpsam@sbcglobal.net

Dave