They’re convinced by the arguments and evidence they’ve been presented with & whatever evidentiary standard or lack of standard to accept the belief. Presenting clear, concise evidence that disagrees with their position may not convince them immediately, but if they are willing to be honest it will effect their confidence and more evidence over time should be more convincing. If it’s similar to deprogramming cult members being confronting or mocking isn’t recommended compared to actively listening, encouraging better standards for evidence and media literacy, and presenting good evidence and why it’s considered good evidence.