Guys,
Take off the WLF and gently remove the screen. You will see three screws that the screen was sitting on. They are adjustable. Clockwise lower the screw and counter clockwise lifts it up. You need a special screwdriver available from Mamiya Parts Center for $70. Alternatively you can buy a $3 one from Home Depot and have a natch machined in the center.
Mamiya use a special ground glass for adjustment however it never worked perfectly for me afterwards.
My approach is very simple. I put my Rz on a very steady studio stand and tether to computer.
I do it with 110mm lens as it works the best. I focus the lens at minimum focusing distance. On a little table a place piece of plywood with nailed diagonal line of 10 nails of different color, spaced about 1/4 inch apart. I focus in the center of the nails and make and image. I examine the picture and adjust the screen until the nail I focus on is the one in focus in the image.
Once I have it, it will translate to perfect focus on any distance with any Mamiya lens.
It takes me about 15 minutes to perfectly adjust a switch to a new screen.
Andre