Does anyone have any go to stretches for this?

I feel like I'm "surrounding" my problem pretty well with scalene and pec stretches, but I don't think I'm getting at the first rib issue (if it is the issue).

My hypothesis is that the posterior first rib may have been the problem from the getgo 18 months ago. I suffered some kind of injury at the gym in the posterior neck/shoulder region and I wonder if the end result was an elevated posterior first rib.

I've seen a lot of youtube videos where practitioners mobilize the first rib, but I want to do this myself. I've seen one example where you grab a pole of some sort, put a towel around the end and essentially stick it into the area of the first rib while laying on the floor. You then push the pole into the wall to push the rib down while at the same time lifting your arm overhead and externally rotating.

Anyways, any help here would be greatly appreciated.

Thanks.

KY