Basically, as always, just try again and again and again. It feels completely weird in the beginning but that changes with experience.
Speed is helping. During the move I fly the kite only with the back hand. Then I fly the kite to the zenith and lean far into the wind. Kind of pushing the bar into the new direction in front of my head. Meanwhile pulling the kite down in the new direction. Before I start the tack I always grab the bar only on one side of the lines. That makes it much easier to pull the kite down while leaning into the curve.
Look at the BRM videos. Greg does them so nicely.