They used time travel to stop time travel, that's different -- if time travel didn't happen, then Voyager wouldn't have been present in the 29th century Sol. Of course it was a paradox, perhaps even a predestination paradox (with 29th century technology kickstarting the computer revolution of the late 20th century)
Kirk of course used Time Travel to kidnap some whales and save Earth, but that wasn't time travel to undo something that had happened.
Picard used time travel to undo Borg time travel (First Contact), or Devidian (Times Arrow). Darvin tried to use time travel to change the past, but was stopped by Sisko and co.
There were localised time travel incidents where a crew member went back in time in some fashion to undo an event they had witnessed - O'Brien in Visonary for example, or when the crew member prevented time travel and caused a paradox (Odo in Children of Time)
Discovery of course also used time travel to save the universe from control, but that was forward time travel, which we all do at various speeds (usually about 1minute/minute, but at relativistic speeds that can change). Backwards time travel isn't a problem.
And then there's the whole "Admiral Janeway" mess from Endgame which is probably the closest situation to a hypothetical Burnham going back in time to save Kweijan. For some reason the time cops weren't interested in those events, perhaps (as I believe suggested in TrekLit) because those actions were critical in stopping the Borg taking over the galaxy, and that counted as more important.
