There is probably nothing that you can actually do about this, as the smell is imbedded into the wood. It will eventually air out and most of the smell would go away. Spraying anything on it will probably harm the finish.
It depends on what type of piano that you have. You should get in touch with your local music store. They have professionals that clean instruments and know how to clean them with out destroying them. For the outside, wipe down with wood polish, that might help.
Vacuum out dust and loose mold. Working in small patches, wipe the wooden parts of the piano with soapy water, then plain water, then dry immediately. Polish with 3 parts mineral oil, 1 part vinegar, and a little tea tree oil. Vacuum, don't rub strings or hammers.
I would take some charcoal (like you use on a grille) and place inside the piano in a bowl or bucket and let it sit for a few days. The charcoal should absorb the smell.