Give yourself a couple days if you have to. Clearing the CMOS erases all settings you had. You will need to configure the computer again. In some cases, this is no big deal. To others, its a nightmare.
Many newer boards have a jumper just for clearing it.
It should be documented in the manual. You flip the jumper, then put it back and the CMOS is gone, hopefully. When doing this, make sure the system is unplugged so that all voltage to the motherboard is gone. The long way is to remove the system battery. If yours is removable, take it out and wait a few hours, then come back, put it back in, and reboot.