1. The method was never revealed.
2. The priests were instructed to heal it with sacrifices.
3. It could only be healed by a miracle.
4. Moses gave the healing instructions in Deuteronomy.
The correct answer is #3.
There were indeed several instances of healed leprosy* recorded in both the Old and New Testaments. In the Tanakh, we begin with Moses (Exodus 4:6-7), then Miriam (Numbers 12:10-15), and Naaman the Syrian (2 Kings 5:1-14). All were healed by miraculous intervention. In the Brit Chadasha (the New Testament), we see another miraculous healing performed by Yeshua Himself. As the Lord had done in the Tanakh, so Yeshua, by His own authority and power, healed the leper. Adhering to Mosaic Law, Yeshua told the leper after restoring him to health: “See that you tell no one; but go, show yourself to the priest and present the offering that Moses commanded, as a testimony to them.” (Matthew 8:4).
For many generations, from the time of Elisha, there were many cases of leprosy, but no Israelite was healed until Yeshua’s miraculous touch in Matthew 8:3. For the first time since that period, the priests witnessed what the Torah never prescribed through human intervention: a cure for leprosy. Yeshua directed the healed man to the priests so they would have undeniable evidence that the promised Messiah had come.
*There were others with leprosy who were never healed: Gehazi (2Kings 5:27), the four lepers at the Gate of Samaria (2Kings 7:3-10), King Uzziah (2Chronicles 26:21), as well as many anonymous ones not healed whom Jesus pointed to (Luke 4:27).