the two holes on the tool fit over the pins on the selector drum and the edge of the tool lines up with a notch on the pawl. this tool has since been superceded by a different one (88713.3334), which i think is much harder to use.
if you’re eyes are good, getting the line on the pawl centred between two pins works fine.
just get a gear lever on the splines and mske sure you can run up and down the gears before putting everything else back in the case.