I think the one upstairs is right. Actually, the key is the knee.
My method is that you must have a big mirror as high as people.
Then you wear shorts at home, preferably trousers.
Just run in front of the mirror.
If your forehand is strong, your knees are pushed to both sides.
If you revise the economy every day, remember that your knees must move forward.
When you go out for a run, pedal hard (but only if your knees are forward)
Practice for half a month every day, and you will correct it all.