This teeth whitening Photoshop action is perfect if you need a guided tour through whitening teeth, but it doesn’t do everything for you automatically.
After starting the action you’ll be told to select the teeth using one of the selection tools. Then click play after doing so to finish the action.
You can double-click the adjustment layer icon called Whiteness and adjust the Lightness to make the teeth as white as you want. Just don’t go too white or it may not look very realistic.