name several informal ways of saying sorry

Through an apology video, apology letter, or even in real life. All you have to do is say "I'm sorry". If this is not the answer you're looking for, then it must be this:

1. I'm sorry.
2. I truly apologize for my mistakes.
3. I am genuinely sorry for what I did.
4. I'm sorry, I promise I won't do it again.