How do you reset the computer in a 2001 Nissan Frontier?
It won't help to "reset" it. the emission system has a problem with it and it needs to be diagnosed.
You can disconnect the battery cable for a few minutes. I had an engine light, fixed and EGR valve diaphragm and then disconnected the battery. It forces the ecu to run a check.
Connect an OBD-II code reader to the port just above the driver side kick panel and use it to reset the truck's computer. These readers are available online for less than the cost of a tank of gas. In the US, AutoZone will loan this tool free of charge (with a credit card) and the light can be reset in the parking lot.