Same answer most of us would give you. Easy fix if you go see a PGA instructor. Could be worked out with one lesson and practice at the range. Hard to fix something you cannot see. especially if you are not a trained professional. With respect.

You're too close to the ball. A PGA professional will be your best bet.

Rotation of the lower body through the swing may be the hardest thing to explain, and the easiest to demonstrate. In all honesty, even as a low handicapper for a few decades, it's still my biggest flaw. I'm usually the first to say not all PGA guys are created equal, find a seasoned teacher, pay a little more, it'll be worth it in the long run. Good luck!

get a lesson

Agree with all the above answers. Lessons with a good PGA pro would definitely help!

If not in a position to book lessons, something that's been helping me with this as of late at the range has been hitting the first 15-30 balls at 1/8th speed, very limited backswing, very limited hip rotation, and just allowing the club to naturally follow the swing plane with proper angles (using a small Alignment mirror from the rear-on view (the ones with the red swing plane line on them)). Hitting them at 1/8th power really allows me to feel the feedback on where on the club face it's hitting with each minor adjustment & seeing the result of the ball flight down range. Then the next 20 at 1/4 to 1/2 speed with a little more back swing and timing the hip rotation with the downswing, impact, & follow through. Then the next 30-40 with a Full swing (and occasionally going back to 1/8th to 1/2 speed hits in between as soon as I have a mis-hit to reset before resuming back to Full swing.

I'm not a pro by any means and probably not qualified to give any tips, but this has been very helpful for me.

Firstly, I agree with going to see an instructor, but understand thats not always easy.

I personally have this same problem, an instructor had me put an alignment stick along the the grip so it extends from the grip in front of your front hip. Then take half swings or even just 30-40 yard pitch shots and keep the alignment stick from hitting your left side as a righty (if you "cast" or extend early you will whip yourself with the alignment stick). Instant feedback, but it starts to sting a little bit if you don't fix it..

It did help me a ton to create the correct feel, and after the second day doing it I was no longer adding welts to my left rib cage. It's my go-to beginning drill at the range.