You can use oxalic acid when trying to remove discoloration or water damaged spots. The entire surface needs to be treated and then neutralized with a clean water wash. Wipe the surface down with clean water and allow to dry completely.

Lastly, finish sand with the appropriate grit paper:

• Oil-based products: 150-grit
• Water-based products: 220-grit

It’s not a bleach but it will brighten the wood back to its original color.