Here's Nikon's article on the auto focus calibration routine.
But I couldn't get it to work very well. Set it up on a tripod in a well lit area. I just used a a book on it's end with a ruler taped at a 45°. Focus on the front of the book (0 on the ruler). Then shoot some shots at the highest aperture of the lens. and see where the focus actually is. Make a manual adjustment +/-..
I found some lenses that were good and a couple that needed a tweak, like my Sigma 15. The D850 is very sensitive...
There's lots of simple targets you can buy too. Google is your friend.