A lot of times in the golf swing, someone’s left arm will break down through the golf ball. This is called a chicken wing. This can happen because someone is coming over the top with their golf swing.
To correct your chicken wing, make a tube that will slide over your lead arm over your elbow. Take a full swing with a three-quarters follow-through, teaching your body how to trust an extended lead arm. Be aware of where your club is exiting. The club should be vertical and pointed over you as opposed to off to the side.
So, get your tube out and learn to trust to extend through the golf ball!