If you have an overexposed photo, the easiest way to fix it is to use Shadow/Highlight. You can also create a new Layer and change the Blending mode to Multiply. This will darken the photo uniformly. You can repeat this until you are happy with the results.
Overexposure is when your image has too much light affecting the highlights and some midtones. You can use Levels: move the sliders so that they are below the black area of the histogram. Alternatively you can use Shadow and Highlights tool in Photoshop. Click on Show more option.
Learn how to lighten dark photos in Photoshop using a few different methods like Screen Blend mode, Levels, Shadow/Highlight and Brightness/Contrast.