How do you get oil light to go off after changing the oil on my Honda TRX420 ATV?

You switch the ignition power switch off, then press the odometer trip button. Hold it down and turn the ignition switch back on. All the time holding down the odometer button for 3-4 seconds. That clears the change oil message and resets the "change oil" interval to "0". So you're good for another 600 miles.