The interviewer wants to hear that customers are your priority. Tell the interviewer that you would graciously stop what you were doing and start by genuinely listening to the customer. Next, share that you would apologize to the customer and take whatever corrective action was necessary. Be sure to mention that most challenging customers do not take much time, and they just want to know that their opinion is being heard. If you have any training in customer dispute resolution, this is a great time to bring this up as well.
"I have received some training in customer dispute resolution and am more than comfortable dealing with angry customers. I know that most people who are upset, need to be heard. I would stop what I was doing and actively listen while showing that I understood the hardship or predicament. I would repeat back what they said to me, and then ask them how I can help."