Speedometer stuck at maxed out position

You are going about this all wrong. Intermittent voltage spikes can cause a gauge to go too high when the ignition switch is off. These are not the extremely reliable spring-loaded mechanical speedometers we had for almost one hundred years. They use "stepper" motors now that are run by a computer circuit. The motor is pulsed with varying voltages and polarities to place it in the desired position. When a voltage spike makes it go past half way, when the ignition switch is turned on, it simply magnetically looks for the shortest way to "0", and that is clockwise. It gets caught behind the stop peg at "0" or at the highest reading on the scale.

The fix is to just drive the vehicle faster than half of the highest reading. Once the shortest way to the desired reading is counter-clockwise, the pointer will bounce there, then follow the speed back down like normal.

An alternative is to use a scanner in test mode and run the gauges through their paces. The final step is to run all of them back down to "0".

It is sounds like the speedometer has gone out and needs to be replaced.

If you physically pushed the pointer to "0", you're done. That's the hardest of the three ways to do it, but the results are the same, assuming you spun it counter-clockwise. Driving faster than half scale is the easiest way to do the same thing. You can also perform the gauge test procedure with a scanner. That runs every gauge to full scale, in steps, then back to "0".

Regardless how you got the pointer to "0", the job is done, and it will work normally unless the instrument cluster is defective.