Oh no! I feel your pain so bad.
Honestly, I would just forget about it. If you're not trying to sell it, it doesn't matter at all... even brand new pianos have plenty of imperfections. This really has no effect on the sound.
Nobody will really get up and look at your soundboard, and if they do, you get to blame the cat.
Trying to touch it up may well cause more harm than good. It's really easy to mess things up unless a professional is involved. Even then, it's likely not worth the time, expense, and toxicity. If a buyer complains, give them a $100 discount to touch it up themselves.
More importantly, play on and enjoy your piano! It's only been further personalized with a unique patina. 🙂
