Apologies are less about hearing the words “I’m sorry” than making sure someone understands the impact his or her actions. Before you say anything acknowledge that the other person may not have meant to hurt or upset you. If you are carrying some responsibility however small, that will put you in a better frame of mind when you approach the other person.
Email is off-limits if you are offering an apology; you should arrange a time for a real conversation, ideally in person, and if that’s absolutely not possible, over the phone. As with most sticky subjects and situations, you want to avoid the word “you” in favor of “I”.
Remember that you may not hear the magic words “I’m sorry”. And that’s okay. Because what all of us really want in these situations is to be heard and understood and to close the conversation with some sort of plan for not repeating the incident or situation. Cheers!