Hi, I am Alexander Parker.
Hello, How could I serve you today?
As I have an emergency work in my office, I have to change my existing  reservation.
Sure, I am glad to help you. Wait a moment I will check with your existing reservation and get back to you.
Ok.
Thank you for waiting, There is no reservation found on your name.
Ok, not a problem. Thank you for your information.
Thank you for approaching  us, Have a good day.