Was/is the air filter dirty?
Does main blower run?
. Good info, that explains more.
Does this unit blow air down or up?
Look at page 22 here to locate and press resets.
That shows you the location of the parts with description. You will notice the location of 3 and 13. I did this to assist you in locating the parts which that page does.
If the switch has a tiny button in the center you simply press it and hope it clicks. If no button is present, the only hope beyond replacement is to tap on the switch and see if it resets itself.
No problem, if you need further help let me know.