A dry finger and time. Rub lightly and some of that stuff will ball up and come off. Eventually the rest of it will wear off.
The correct fix is to remove the original film and apply a new one. It'll cost a few bucks, but it'll look andd work better. (BTW, most bubbles that you can't rub out are microscropic particles of dust, so use transparent tape to pick all the dust (even where you can't see any) off the screen before putting a screen protector on it.)