Repenting for speaking Lashon Ha-Ra

Q: If another person is unaware that one spoke Lashon Ha-Ra about him and he wants to repent, should he tell him?
A: The Chafetz Chaim in Hilchot Lashon Ha-Ra (4:12) wrote that if one wants truly repents he should tell him even though he will causes him further pain. It is taught in the name of Rabbi Yisrael Salanter, however, that one has no right to cause another pain so that he can do Teshuvah.