What is the ruling on profits resulting from sales of "what I do not possess" that occurred before I became aware of their prohibition, and how can one dispose of them?

Since you were ignorant of the ruling, there is no sin upon you for the profits you earned, and you may benefit from them. This is supported by what is mentioned in Ibn Taymiyyah's "Al-Ikhtiyarat," the saying of Ibn Uthaymeen, and the noble verse: "So whoever receives an admonition from his Lord and stops, then he may keep what is past, and his affair is left to Allah." However, if he was aware, he disposes of the usury by giving it in charity.