How can I repair the sin of lashon hara?

Hello, 

The repair is through regret over the sin, verbal confession as explained below, and a commitment for the future not to return to this sin ever again (Rambam, Hilchot Teshuva, chapter 2, halacha 2). Verbal confession means that one must say, "Please, Hashem, I have sinned, I have done wrong, and I have rebelled before You, and I did such and such, and behold I regret and am ashamed of my deeds, and I will never again return to this matter" (Rambam, there, chapter 1, halacha 1). In addition, in principle you need to appease him so that he will agree to forgive you, because for transgressions between one person and another, Yom Kippur does not atone until he has been appeased (Shulchan Aruch, siman 606, seif 1). However, if he does not know that you spoke lashon hara about him, and it may be assumed that knowing this will cause him pain and distress, you do not need to tell him the story in detail. Rather, you should tell him that if you hurt him, you ask forgiveness for everything, and that is sufficient (Rav Moshe Sternbuch shlita in his sefer Mo'adim U'Zemanim, part 1, siman 54, who heard this from Rav Eliezer Dessler zt"l בשם Rav Yisrael Salanter zt"l. וכן ruled in the sefer Chazon Ovadia, Yamim Nora'im, page 244). 

Much success, 

Hillel Meirs