Clearing cmos

The BIOS battery maybe under one of the panels on the bottom of the laptop or under the keyboard.
To reset the BIOS ack to the default settings, go into the BIOS configuration and look at the various configurations, usually there is a setting to load the Default settings, then save and exit, and this would not change the Date & Time setting.
The other way to set the BIOS default setting is to remove the BIOS battery (it is probably a lithium 3volt button battery), wait 1/2 hour and replace the battery, the go into the BIOS configuration and set the Date & Time setting etc.