How did Scott Bacula learn how to round house kick?

Possibly he already knew how from previous training, but more likely he hired a trainer to prepare him for the role (as any ambitious actor does who wants to be successful in whatever role he/she aspires to).

I doubt he had to hire anyone personally. Once the scene is written into the show, they have to choreograph the fight and teach him how to do it convincingly. This would come out of the Quantum Leap budget.

If you were an actor, and your job was practicing that kick for hours and days, you would nail it, too.

I take a martial arts class and a lot of people (not me) have beautiful form. It’s really fun to watch. And this is at an insignificant school, they are just average people off the street.

Starfleet Academy

Body Double plus post production?

He was in good shape, good weight, exercised and ate in a healthy manner before training. The he was taught the moves, and practiced.

You can do the same by losing weight, exercising, getting in shape and eating a healthy diet. After you get in shape, a martial arts coach can teach you the moves. It may take a while, but it is possible.