Resetting the prop valve on a new sysytem

[my new 72]

Just what the heading says. I am replacing the whole brake system except for the prop valve because it is only a year old and still works, but I noticed when I took it off, the valve was not centered, meaning that there was no fluid being pumped to the rear lines. When I put everything back together, how do I reset the prop valve and bleed the brakes properly? Thanks for all the help in advance.