The Black and white you see is just the cameras representation of the "raw" pixel information straight from the sensor. The RAW file format has yet to undergo demosaicing, and so it contains just one red, green, or blue value at each pixel location.
Lightroom, or any other RAW processor, doesn't recognize the in-camera processing because it is unique to the camera.
If you want black-and-white images straight from the camera, either shoot JPEG or use the software that came with your camera. If you shoot raw, then you use the black-and-white features in Lightroom.
use the black-and-white features in Lightroom.
Here is a start-
Select all in Library Grid view [CTRL+A]
Undo with [CTRL+Z]