If you are referring to the green/yellow/red indicator, there should be a
key hole at the bottom left of the instrument cluster near the tachometer.
Stick your master key in this hole to reset it to green.

If you are referring to the amber "check engine light", I normally remove
the "back-up" fuse (under the hood) for about a minute.  After putting it
back in, the clock and radio presets will have to be reset.