High limit switch open on armstrong furnace. I have an Armstrong Air furnace that is not blowing

Question

I have an Armstrong Air furnace that is not blowing hot air. Noticed the LED light is flashing four times, which, according to the alarm code means I have a high limit switch open. Turned the furnace off and back on but that didn't do any good. How do I find and manually close/reset the high limit switch??? Thanks!