Master Hutton has a beautiful Dollyo Chagi and this is how he trains it.
Use a chair to hold on to for balance, understand the direction and trajectory, then start working the muscles needed to execute the kick. Note the role the arm plays to counter-balance the action of the leg. Make sure you retract each turning kick with the heal coming back to the glutes.
This free clip is part of a Taekwon-Do coaching session by Master Mark Hutton