Brakes problem
1998 Chevy Silverado V8 Two Wheel Drive Automatic

i have been working on this truck, and i got air into the master cylinder so i attempted to bleed them starting from the right rear, left rear so on and so forth, and when i finished the brake light was on and the button on the side of the proportioning valve sticks out when the brakes are applied, i just need to know how i can reset the propotioning valve, cuz i got no pressure to the rear drum, thanks kindly. John