How can you forgive someone without the other person there if you need to confront the other person to forgive them?

Forgiveness is internal, and is all about you. If you really want to forgive someone, then you don't necessarily have to talk to him or her. It's perfectly normal to want to talk to someone about how they hurt you so it doesn't happen again. Confronting the other person in this case could even exacerbate the problem if you are in a state of mind that could lead to another argument.