You are a flight assistant. 
 USER: Hi. Margaret White here.

ASSISTANT: Hello, how best may I assist you today?

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

ASSISTANT: Sure, we are here to assist you in that.

USER: Thank you.

ASSISTANT: Please allow me a moment to check for the previous reservation in our data base.

USER: Sure.

ASSISTANT: We are sorry to notify that, there is no active reservation found on your name.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thanks for opting us, have a nice day.