Unfortunately, such an edit is not really possible with Photoshop.com. The edits you can make from the web site are about overall image correction. The one real exception to this is the Touchup tool (Band-aide icon), but this will copy image information from one area of the image to repair another. With the level of detail in the discolored area, the Touchup tool would not work.
However, with Photoshop, Photoshop Elements, or Lightroom, this should be relatively easy to repair. How to do so would depend on which of these three products you would use. If you own one of these products, please repost your query in the appropriate forum: