Ideally, a debate would be best. The challenge is that it's very easy to make false statements. It takes very little effort. You can "Gish gallop" your way through a discussion and the other side is forced to refute every single false statement. A lot of conspiracy theories spread and are believed because their narratives are so simple and easy to understand. Showing that they're wrong takes a lot of explaining, which often strengthens the conspiracy. I can't say I have a solution to it, but it's worth recognizing that discussion doesn't, unfortunately, always work to educate the masses.