Hi. I am Janet King.
Hello, how can I help you?
I need to change my existing reservation as my exams got postponed, Can you please help me with that?
Sure, I am willing to help you.
Thank you.
Please wait a minute I will revert to you.
Sure.
Thank you for waiting, sorry to inform we didn't find any reservation on your name.
Ok, no problem. Thanks for your information.
Thank you for opting us, have a  nice day.