It's easy just like OPatience says---just remove the panel under the glove box and
it's right there in front of you.
You might want to remove the plug-in connector and get a
test light to be sure you don't have some kind of bad connection under
there rather than a bad motor.
Also you can check the heater motor relay which is in the
central junction box, marked C-2017, under the dash on the left
(driver's side). The relay is cheap, if you want to take a guess that
that's the problem, if the heater motor bench tests