I hit low and left for years. Some things that helped me were 1) keeping a really tight grip with my support hand 2) relaxing my trigger hand/finger 3) shooting at 2" dot instead of silhouettes. Relaxing the trigger hand/finger is the tricky part. I just kind of let my mind go empty and focus on the sights. The part of the pistol that I "feel" the most is where my left (support) hand that presses against the edge of the backstrap. Hitting the 2" dots took a lot of concentration at first. It's easier than it was a year ago and I'm faster. I spent lots of time shooting at 3x5 notecards too, but for whatever reason the dots have helped me more than the cards did. I'm by no means a great shooter, but I'm a lot better than I was a couple of years ago--even one year ago.
Also, pay attention to where the bullet impacts relative to your sights. If you think the bullet should hit top of the front sight at 7", but the sights are really set for "drive the dot" at that range, then you'll always shoot low regardless of your flinch. It took me longer to fully appreciate this last point that it should have.
Lastly, shoot some ball and dummy drills. Load a mag with alternating live and dummy rounds. Shoot a live round, "shoot" a dummy round, tap rack, shoot a live round, repeat. This is not fun, but I think it helps. Right now I have a friend with a terrible flinch, but he refuses to do this because of how much it highlights his flaws, which, of course, is the point of doing it.