Locate the two metal holes on the back of your shoulder pads. The holes should be on the bottom of the back shoulder pad plates.
Line up the back plate holes with the ones on the shoulder pads. Align the holes up or down until the back plate covers your lower back.
Insert screws through the aligned holes on both the back plate and the shoulder pads. Make sure the screws are locked in tightly.
Repeat the process of screwing in the bolts or screws if the fit is not right or if slipping occurs. If the back plate is not installed properly it can be more of a hindrance than a help.