Genuine answer: one mind and one heart at a time. With any luck, some of them become influential and the message spreads more rapidly.

Religious indoctrination is hard, because so many of them teach that indoctrinating others is a way to save them. Ultimately, however, the whole belief system is a house of cards. It takes surprisingly little to bring it down. Ask them how they know that what they believe merits their belief. It starts there.