You can't do either of those things at the moment.  The way it works now is that nitpicks are not voted on, but are automatically accepted.  To vote on whether you like a particular nitpick or not, you find that nitpick.  It's a lousy system, obviously, and one that Rick (Wastech) has promised will be changed back to the normal way.  (It's not clear why they bothered to write code for a system they weren't going to use.)  He hasn't said anything about previously-submitted nitpicks, although people have brought it up to him.  Check in the "Glitches" thread for more discussion on this.