How do you use the item Sacred Ash in Pokemon Heart Gold?

You don't use the item "Sacred Ash" in Pokemon Heart Gold. There is no item with that name in the game.

There are items that sound similar, but they have different purposes:

* Sacred Ash: This is a item in Pokemon Black 2 and White 2 that is used to evolve the Pokemon Litwick into Lampent when traded.

* Charcoal: This item is used to evolve Slugma into Magcargo.

* Everstone: This item prevents a Pokemon from evolving.

If you are thinking of a different item, please clarify its name and I can help you figure out its use.