I've engaged a few flat earthers to actually listen to their arguments and show them my own evidence that it's real (locating amateur radio satellites using data shared by people around the globe and demonstrating the doppler effect on them). The response strikes me as being indicative of mental illness. And I don't mean that as an insult - I mean that when confronted with that they're clearly irrational. And somethi…
I found the best thing to do is stop there. Just listen, observe, try to understand. Be patient.
Unless someone comes to you asking a question, you're unlikely to change anyone's mind immediately, and even if they are asking opinions often change slowly if at all.
When we tell people they're wrong, we push them away a little, and our sphere of influence diminishes.