Editing the post dismisses "very low quality" flags as disputed, assince the act of editing contradicts the flagger's statement that the post cannot be salvaged.
Casting a close vote dismisses canned flags on a question, i.e. close(close flags from users with <3k rep and very low quality) on a question as helpful.
If the post ends up deleted, all flags are automatically dismissed as helpful. This can be achieved either by casting the final delete vote or the decisive spam/offensive flag.
Dismissed for real, that is. Actions like upvoting/downvoting or flagging only hide the post from your own 10k queue.