Step 3 
Mouse over your image and use the left and right bracket keys to make your brush larger or smaller according to the area you’re working on, then paint in your effect. Moving the sliders before you paint on an adjustment can be a bit of a guessing game. So go with the default, then, after painting, readjust the Exposure slider to further decrease the exposure in the window’s view. If the location of the adjustment you painted isn’t right, erase some of it by clicking on Erase in the Brush menu and paint out the adjustment where it doesn’t belong.