from the ZR1.net
http://zr1.net/ZR1_techtips.html
Tip #17: Engine oil life Monitor
To reset the oil life monitor:
A. Turn the key to the "ON" position, but don't start the engine.
B. Press the "ENG MET" button on the trip monitor and release. Then, within five seconds, press and release the "ENG MET" button again.
C. Within five seconds of Step 2, press and hold the "RANGE" button on the trip monitor. The "CHANGE OIL" light will flash.
D. Hold the "RANGE" button until the "CHANGE OIL" light stops flashing and goes out. When the light goes out, the engine oil life monitor is reset. This should take about ten seconds. If it doesn't reset, turn ignition "OFF" and repeat the procedure.