Hello, It's great you are preparing to have the right customer mindset! I agree with the feedback already provided - listening and empathy are keys to diffusing a difficult situation. I, too, work in a role which is the last resort for customers in our company. Doing the right thing for the customer in our culture is always supported by our leadership. Often if a customer just feels someone is truly listening to them, understands their problem, and takes ownership they will calm down. That sense of ownership is key. By the time they are frustrated enough to reach that level of escalation, it is often because others have not taken the responsibility or assumed the "it's not my job" position and passed the problem down the line. Let the customer know you will stay in contact with them until the problem is resolved and then make sure it is resolved. If you make a commitment, keep it and hold others accountable for keeping theirs. While a customer is ranting, stay focused on the outcome and try to keep them moving in that direction. "I can hear you are frustrated by this experience, but my job is to make this right for you." Be confident in knowing you will be able to help them through this situation and that will keep you both moving in the right direction.
Good luck! Great customer service is hard to find these days so I'm glad to see someone thinking along these lines so early in career.