You can redirect a discussion by "bridging" – stating what happened in the past, what is happening now, and what you plan to do in the future.
For example, a customer asks, "How could you fail to deliver my shipment on time? That was the worst mistake I've ever seen." You might say, "A mistake was made in delivery and we take responsibility for it. We found the shipment and it will be there today with our compliments. We'll be reviewing our procedures to see what changes need to be made so this won't happen again."
–The Customer Service Advantage