Your user manuals don't actually show this at all but...cmos is pretty recognizable and unmistakable. It's a flat battery about size of a dime lying on the board. Should look something like:
https://computing.which.co.uk/hc/en-gb/article_attachments/204321729/CMOS_battery.png
Just open up the side of your computer (after you've shut it down), and make sure you do not touch your mobo with your hands, without touching them to a grounded metal surface first (like metal parts of your computer case).