When you were undergone training free style swimming coach said do not bend knee But you see at Olympics free style players bend their knees while swimming What is the correct way?

it depends on what stroke you are swimming. if you are swimming breaststroke then you do bend your knee in freestyle and backstroke you don't bend your knee. in butterfly you only snap your whole leg your knee doesn't bend all the way. if you don't kick the right way in breaststroke then you can hurt your self becareful and ask a coach. good luck