You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: I am Dennis Collins. My exams have postponed suddenly, so I want to change my existing reservation. Can you please help me out?

ASSISTANT: Sure, please give me a minute.

USER: Ok.

ASSISTANT: May be your ticket is not booked properly. That's why, I didn't found any reservation with your name.

USER: That's ok. Thank you for your information.

ASSISTANT: Thank you, have a nice day.