The Steadicam® is a three part system: vest, arm, and sled.
The vest distributes the weight of the system evenly onto the operators body. It must be properly sized and adjusted to fit the operator.
The cross back straps are sandwiched between the shoulder pads and vest back, and secured with Velcro®.
Adjust the position of the upper straps so they end as shown in the photo (fairly low). In this position, they will be easy to clip, unclip, and adjust.
Note: These vest parts are typical, but may look or work ...