If it's dust and if your screen protector's adhesive is static-cling, it's easily removable. Take some scotch tape, press it to a corner of the screen protector, and lift it up (don't "pick" it up with your finger or a toothpick or something, as this will probably damage the screen). Then take another piece of scotch tape and press it to the dust. The tape should fix that right up without getting fingerprints and oils all over the inside of the screen. Then all you have to do is lay it back down and rub out any air bubbles.
But if it's a matter of the shield being crooked, well nothing'll fix that but a re-do.