They should counter misinformation with actual information, not censorship. By censoring something, you defacto breath life into it as opposed to just denouncing it.
That's been the go-to strategy for decades now; the problem is that it doesn't work.
The speed at which news (gossip, really) spreads on social media is proportional to how effective it is at getting social media users to re-post it, rather than proportional to how accurate it is.
The problem with that is that the truth is sometimes compelling but often not particularly interesting, while a well-crafted lie is (by definition) always compelling.
Therefore we constantly see the scenario where "a lie can travel halfway around the world while the truth is still putting on its shoes". Usually by the time the ethical people have posted their followup corrections, it's too late, the damage has been done and half of the Internet thinks the lie is true and the corrections are "just a cover-up".
I don't have a solution for this problem, I can only unhelpfully note that simply "drowning out the lies with the truth" isn't a solution that works anymore, if it ever did.