Play the long game. Recognize that you can't reshape their worldview in one conversation.

Ask them how they know what they think they know. If their source is mainstream media, you can ask, "Do you trust that they reported accurately?" They'll probably say something like, "Well, I trust them more than the conspiracy theorists online." And you can say, "But that's not what I'm asking."

Try to find common ground. Most people can see the grain of truth in your views--if you're willing to see the grain of truth in theirs.