Shulchan Aruch Chapter 606:
Note: The REMA is in brackets 
1. Sins that are between one and his fellow, Yom Kippur does not atone for unless he appeases him (receives forgiveness). Even if he only injured him with words, he must attain forgiveness. If he does not forgive him at first, he must try again and go to him a second and a third time. On each attempt he should bring with him three men. And if he does not forgive him after three attempts, he is unable to force him to do so. [However, he should say afterwards before ten men that he wants that person to forgive him.] And if that man is his Rabbi, he must go to him many times until he forgives him. [The forgiver should not be harsh in forgiving if he does not want to give in to the requester’s plea. If the requester gave him a bad name (הוציא עליו שׁם רע), one is not obligated to forgive him.]
2. If the man to whom you have sinned against died, then you bring ten men and you stand with them by his grave. You say, “I have sinned to the L-rd of Israel and to this person (insert name) whom I have sinned to”. [The custom is to ask forgiveness on Erev Yom Kippur (מרדכי דיומא)]
3. There is a decreed ban from earlier generations to not bring a bad name (להוציא שׁם רע) onto dead people.
4. One may ritually immerse himself (טובל) and strike oneself with lashes whenever one wants; with the exception that it should be done before nighttime. And one does not make a blessing on the immersion. [A man only needs to immerse one time without saying וידוי (the confession) because of קרי (emmissions). The same applies if a man washes with nine קבין of water, which also helps. If one’s close relative died between Rosh Hashanah and Yom Kippur, it is permitted to wash and to ritually immerse oneself on Erev Yom Kippur, since Yom Kippur bypasses the seven (days of She’vah). Even thought we have the custom to not wash all thirty days (of mourning), an immersion for a Mitvzvah is permitted. ]
Translated by Jay Dinovitser www.shulchanarach.com
 See Leviticus 16:30
 M.B: However, he may try more attempts than three.
 M.B: This is done to publicize the matter so the individual should soften up and forgive him. (This does not act as forgiveness for the sin, since only that individual may forgive him.)
 Even if he is not his real Rabbi, but he heard from that individual words of Torah.
 M.B: If he wants to forgive him, then he should do it immediately, without being harsh since whoever is virtuous beyond his natural traits, G-d skips over all his sins. If he does not want to forgive him, then he should just tell him so. He should not be cruel if does not want to forgive him anyways, so that his heart should not be accustomed to such behavior. [Kitzur S.A. writes that this is a trait of Esau and not a trait of Israel Avot 5:11 says that one should be hard to anger and easy to please.] And it appears that he must also remove the hatred from his heart when he forgives.
 According to the K.S.A., they answer “you are forgiven” three times.
 According to the Kitzur Shulchan Aruch, if one insulted someone who died, he should ask forgiveness in the place where he insulted him. If he made a bad name for the dead person, he must also repent for transgressing a Rabbinical ban.
 It is a Mitzvah to do so.
 M.B. even unmarried men and girls should go since some opinions state that the act of immersion is part of repentance. The Kitzur S.A. says this is just like a convert requiring a ritual bath.
 Like taking a shower. My Rabbis say that this only works for a man, since we don’t have the custom to follow Ezra’s decree on “keri” anyways. It definitely is not equivalent to a ritual immersion and does not work for women according to all opinions. A “kav” is a unit of measure. Each “kav” is approximately 2.2 Liters.