I think it's better for you to research the YouTube library. It's far better explained there. And there are tons of judo videos of how to make your opponent help you execute the throw.
What I meant to cover before is, to push him aggresively but for you to stay balanced while doing it AND the goal is to make him resist the push , in such a way, all you have to do in that golden moment is to pull him slightly(it's what you normally do when entering the harai goshi) that will make him lean abit forward losing his firm balance and which will make him easier to be thrown. You only have that moment though to execute the throw, that's why the execution have to be smooth and drilled a 1000 times before during practice.
Still, I encourage you to check out the videos on YouTube regarding the various ways to set up a judo throw