My typical method of helping with this is to find common ground. Find something you both agree on, even if it’s only tangentially related, and then pose an argument and phrase it as such.

For example, when discussing if the Earth is flat or round, you might both find agreement in that nobody has ever fallen off the edge of the Earth. Then you might try to pose an argument as to why - which is more likely, that nobody has ever traveled far enough to fall off, or that the earth is actually a continuous plane?

I find assigning probabilities to topics often helps.

But sometimes you can’t, and that’s when you agree to disagree and politely exit the discourse.