Sorry is a down payment. The rest gets paid in what you do differently.

An apology opens an account rather than closing one. The words matter, but they are a statement of intent, and intent is the part that is cheapest to produce. What settles the rest is a stretch of ordinary time in which the thing does not happen again, and that stretch is the only evidence the other person can use.

Pick the specific behaviour that caused it and change one visible thing about how you handle it. Tell them what the change is, then let them watch. Do not ask whether you are forgiven yet.