1. Listen. If they are willing to take to you, take the time to hear them out and allow them to express all of what they are feeling. Focus on listening and not readying yourself to respond. We tend to rush to fix things or defend ourselves, but before resolution there should be understanding.
2. Empathize. You don't have to agree with the other person's viewpoint, but you do want to show that you hear them and you care. Try using language like, "I hear what you're saying" or "I see what you mean." You don't have to accept responsibility for something you don't agree with but you can attempt to relate.
3. Work towards a solution. It's helpful to ask, "what can I do to resolve this?" as it's helpful to invite them to be part of the solution rather than making assumptions and telling them how you'll fix it.