Theoretically speaking, if you had to un-brainwash billions of people who have been propagandized for decades, how would you do

Theoretically speaking, if you had to un-brainwash billions of people who have been propagandized for decades, how would you do it? Would you abruptly tell them they have been brainwashed? Or would you slowly introduce this reality to them and show them proof along the way? Источник: BioClandestine