You can't. Not effectively that is.
Other answers are telling you to simulate static throws. I avoid teaching static throws, generally. Moving drills are the most effective in my experience.
Timing is crucial. Reap the foot just as he is placing his weight on it.
Ko Uchi Gari, Kodokan Judo, page 69
You can't do a proper Ko Uchi Gari without having the proper timing. You cannot develop this timing when training by yourself.
All of your technique should have a timing element.
We once had a guy come in and tell one of our teachers that he was a black belt. This dude had never taken a Judo class before. I don't know what books he had read or drills that he had done (if any).
Self-taught self-trained Judo black belts don't exist.