Attrition and radical empathy.

That’s the only thing I’ve seen work. People that far deep need a consistent message that is always transparent and empathic with their emotions. This will erode the core beliefs until the cognitive dissonance between what they are told the opposing message means and what the proponents of the message actually display cracks an opening for self-assessment and reevaluation.

This is why bigotry and fascism work on the premise of ultra-individualist isolationism. Same why cults first line of recruitment is to isolate the individual from society and their previous social network. You can’t get your beliefs eroded if you never have contact with people who think different than you.

Once they get in contact with the people they were told to hate and realize that said people aren’t the monsters they were told, and that their ideas are actually logical and consistent, they can find a socially approved permission to question their preconceived notions and admit fault. Unfortunately, achieving this conditions can be challenging, and it is also why algorithmically curated propaganda (social media) is so effective at spreading hate and misinformation.