To do the desync peak you need to bind your quick leans to your mouse buttons (ex. mouse3 and mouse4 side buttons). Once you have your keybinds set you need to start off by
1. holding alt while aimed in
2. while simultaneously holding alt tap A and quick lean right
these 2 steps are super easy, just keep doing these steps, play around with it in shooting range to get it down. This glitch works because your confusing the game into thinking your trying to slow lean left and quick lean right at the same time. for some reason the game throws your character into the quick lean animation fairly faster than if you were to regularly lean.