How to light up the monochrome background of photography and how to set the white balance of the camera?

First of all, correct it. It's not 17%, but 18% medium gray board.

Use the camera's automatic white balance to shoot a blank sheet of paper first, then shoot a full picture against this blank sheet of paper first, and finally set the white balance to be customized, just choose white paper to shoot, and then you can't go wrong in any case.