Look for three jumper pins on their own on the motheboard, probably near the 3V battery. The battery is about 20mm or 3/4" in diameter, you can't miss it.
Typically, pins 1-2 will be bridged by a jumper. Remove the jumper and place it over pins 2-3 for about five seconds. Replace back on pins 1-2. CMOS will now be cleared (reset).