For establishing muscle-mind connection I'd recommend light weight, moving very slowly, and doing exercises one arm at a time so you can put your other hand on the muscle you're trying to activate.
Chest flys might be a good choice:
I looked quickly at your video. It’s not possible to give a definite answer based on a single movement but here is what I think.
Your left side (left on video as seen from the back) recruits your upper traps. This is typical of a shrug. Your right side does not or at least not as much.
This probably means your left side lacks some muscles and your trap has ...