He doesn't.
If anyone else has followed the way Putin has dealt with the media in Russia during his tenure Trump is doing the same but just loads more blatant (like everything he does).
The underlying premise is that you undermine the public's faith in all media and actively push out factually incorrect 'news'. Some of the stuff is blatantly false, some not so blatant, some believable and some actual factually correct news, Good or Bad. In that environment it becomes, over time, impossible for the people to spot the difference.
The objective is obviously to control the media by way of controlling the narrative. Something that was less complicated in the days of the print media (With Hillsborough the shining example in our lifetimes). Putin has even been found to be indirectly funding many of the dissenting groups within Russia. Arranging protests and so on.
The 'goldengate' scandal was the perfect example. In his press conference which should have been about his business affairs, possible collusion with foreign powers and the billionty stupid things he's said and done, he managed to totally control the narrative and like I said REALLY BLATANTLY when he shut down that journalist. Apart from the scary/masterful way he dodged any questions about his business dealings by sending that lawyer out to filibuster for 15 minutes, he spent the rest of the time basically discussing whether some post on reddit was true or not and everyone seems to have lapped it up. It's sexy, it's miss world, it's like Bond, in Russia with miss world only it's also really gross and voyeuristic and even if you don't believe it we'll all remember it more than what that lawyer said and that's the play.
I think if you look back at the bit where he says the story is false he is utterly believable. When the journalist follows up with where it came from he starts his usual distraction nonsense and looks rather shifty. I think that tells it's own tale to me.
Get used to it too because this is how he's going to play it for as long as he lasts.