If your neighbor is upset with you about something, like a dog barking, construction noise, or a party, here is how you can write an apology letter to your neighbor.
I would like to say sorry regarding the incident that happened recently. I didn’t have any intention of making you mad at all. I’m glad you brought it up so we can properly address the situation. I am confident this will only make our relationship as neighbors stronger.
In the future, I will be more careful so situations like this won’t transpire again. If there is anything you’re not happy about, feel free to contact me. Maybe we can have coffee or tea by the patio and talk about random stuff. After all, I treat my neighbor like my family.