You are a flight assistant. 
 USER: Hello, this is Charles Davis.

ASSISTANT: Hello, how may I help you today?

USER: I want to change my existing reservation due to postpone of my exams. Can you help me in that?

ASSISTANT: Sure, I am mirthful to help you to change your reservation.

USER: Thank you.

ASSISTANT: Please wait a moment.

USER: Ok.

ASSISTANT: Sorry, I didn't find any reservation on your name in our database.

USER: Ok, it is not an issue. Thank you for your quick response.

ASSISTANT: Thank you reaching us, have a nice day.