Okay, but if I see something shared that I know to be false and can demonstrate to be false with links to robust summaries of evidence and argument from trusted

Okay, but if I see something shared that I know to be false and can demonstrate to be false with links to robust summaries of evidence and argument from trusted sources then how do I respond? The Facebook model is that I have no real alternative except to share opposing views with others in my bubble. It is fine for your grandpa to talk to racists, but if he shares his newfound junk with me then I should be able to flag it and link the truth such that any viewer of his posts can see how others see it.