In a proper open connection there is a slight constant pull between the partners. You should both have a slight force away from each other, and have a connection that is governed by your back muscles that is keeping you both from moving backwards. To make the follow rock-step (on their right foot), you then make sure their weight is on their left foot (by putting your weight on your right foot) and then loosen that connection. If you are both doing it right, then that connection will be weakened and the force back will make them go backwards then, because they're on their left foot, they will have to step on their right foot. To make it a rock-step, you can't give too much slack and immediately ask for the connection again without moving forwards yourself. This will make the follow step forwards again on their left foot.

I find it easiest to start by doing a rockstep yourself on your left foot without letting you connecting hand move at all. The only way to do this is to loosen the connection and ask for it back in the timing needed.

In any lindy hop move, you should never be moving the follow or pushing/pulling them around. Everything comes from a good connection and an understanding of how momentum works. With a good connection, you will quite literally feel the follow's hips as an extension of your own. You won't have to try to make something happen, because at that point leading a movement is just like moving your arm, it just happens. You can lead anything from open with that connection, you can even lead swivels while keeping the connecting hand completely still. It looks so dumb when a lead tries to lead swivels by doing that weird hand-floppy thing, it shows they don't have a good connection.