There's no one-size-fits-all answer because it completely depends on what the apology is about. However, you can say something like, "I understand you're still upset with me and that I've hurt you deeply. I just want to let you know that I want our relationship to continue, and when you're ready to talk, I'm ready to listen. And I apologize again." That way, they'll know that you aren't going to just turn your back because they haven't forgiven you yet.