I believe this is done one of two ways.  First, check the inside fuse panel to see if there is a push-button type relay located in it.  This will be red and when depressed it will reset the oil life indicator.

The other way is through a system of key on/key off cycles combined with ignition pedal pressing.  My grandfather's Cadillac required you to turn the key to start (but not crank the engine) and off five times, while pressing the accelerator pedal slowly all the way to the floor and releasing it.  

To reset the light, turn the key to the position just before the vehicle starts. (when all system check lights lite up.)  Press and Depress the gas pedal four times completely.  Then turn the key all the way back, like you are gonna take your key out.  Wait Two seconds.  Then turn key to on position just before truck turns on.  You should hear three ring tones.  Always works on my silverados 99-2006.  Jiffy Lube taught me how.  Let us know if you are successful!