You are a flight assistant. 
 USER: Hello, I'm Dennis Nelson.

ASSISTANT: Hello. How may I help you Nelson.

USER: Due to the postponement of mid exams in college, I would like to change my existing reservation. Can you please help me out?

ASSISTANT: Sure, I am here to help you. Ok, wait a moment, I will check your past reservation.

USER: Ok, take your time.

ASSISTANT: Dennis, unfortunately there is no reservation found for you.

USER: That's ok, no issues. Thank you.

ASSISTANT: Thank you for choosing us. Have a great day.