So as not to bog you down with too much detail.
And reading how to do a flip turn isn't the easiest task in the world but it beats trying to write it all out!
OK,momentum into the wall is key.
Throw your head down (because your body follows: key concept in swimming).
It's a flip not a tight six year old tumble. Legs bent at 90's angles = power.
Plant feet shoulder width (squat / jump position) apart at either 10:00 or 2:00 depending on which side is dominant.
Feet should be about two feet below the surface of the water on the wall. WHere you plant them sets you up for the streamline and direction you push off the wall. If you're all loopy pushing off - somethings wrong with where you're planting your feet or how you're planting your feet.
Backstep: hands propel body thru the flip stopping at the head so as to begin streamline once feet hit at 10:00 or 2:00.
Jump off wall (increasing the momentum / speed you had coming into the wall) on somewhat of your side (10:00 / 2:00) rotating to streamline position.
Begin slight kick and repeat at each wall.
Don't fear the wall. You'll hit it with your heels at least once. I did it two weeks ago. First time in years but that's how it goes.
Practice flips away from the wall.
Do not practice turns inside of the flags. Start back far enough to gain momentum. It's the only way.
Try:1. See flags. 2. Breathe. 3. Take a stroke. Flip.
Now keep doing it until you get close enough to actually hit the wall with your feet.
Old school but it's accurate: