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Manually reset it, Should be on an end, possibly by the wires hook up at the body of the roll out switch. You can also move the sensor a little further away from the flame if you have nuisance trip outs.
Roll out switches are normally by the main burners, it should have a sensor wire that runs length wise, in case the main burner flames back out of the chamber the roll out will sense the flame and open.
Main burner assembly, it would nave to sense the burner flame look at the wiring diagram to verify that is exactly what it's called. How do you know it's a roll out switch might be called something else and I'm concentrating on the wrong control.
Diagram may have the color of the roll out switch wires, you can use that as a guide. Should be two wires somewhere near your main burner
Here is a link for what it looks like: http://www.askmehelpdesk.com/heating-air-conditioning/pilot-light-our-lennox-g40uh-x-series-furnace-wont-light-422228.html