That's like asking a dentist the safe way to fill your own cavity. Odds are an untrained person will do irreversible damage. If the "green" corrosion is very light it may be salvageable. If it's a valuable piece. I offer conservation services that may be worth it. To illustrate: I was doing an appraisal for a lawyer in Bronxville who purchased a commercial coin product over the Internet to clean an uncirculated 1884-S Morgan Dollar, which had a value of $7,000. His efforts removed the toning and rendered it into a "details" coin worth $200.