I don't know how much time you have to teach this, but if there was a lot of time, I would first have the students relate personal experiences where an apology was deserved. The stories can be made up, of course.  I would introduce some set phrases that we use for apology notes. "I'm terribly sorry." "I'll make it up to you." "I'll never do that again." "Can you forgive me?"

Next I would have them pair up and write an apology note for each other's story.  Example:

A: My story is that I was mad at my brother and tore up his homework that was due the next day.  He had worked hours on the homework. My mom told me to write my brother an apology.

B. My story is that once I pulled my sister's hair so hard that she cried. My dad told me to write her an apology.

Then A writes B's apology, and B writes A's. They give their apology notes to each other. A and B can then change it and tell why they made the changes. Volunteers can then read their apology notes to the class.