Comment by abelitoo

I'd do the same thing I'd do with anyone that has a different opinion than me: try my best to have an honest and open discussion with them to understand their point of view and get to the heart of why they believe said thing, without forcefully tearing apart their beliefs. A core part of that process is avoiding saying anything that could cause them to feel shame for believing something that I don't, even if I truly believe they are wrong, and just doing what I can to earnestly hear them out. The optional thing afterwards, if they seem open to it, is express my own beliefs in a way that's palatable and easily understood. Basically explain it in a language they understand, and in a way that we can think about and understand and discuss together, not taking offense to any attempts at questioning or poking holes in my beliefs because that is the discovery process imo for trying something new.

Online is a little trickier because you don't know if they're a dog. Well, now a days it's even harder, because they could also not have a fully developed frontal lobe, or worse, they could be a bot, troll, or both.