You are a flight assistant. 
 USER: Hi. I am Gary Hill.

ASSISTANT: Hello. How may I guide you today?

USER: I want to change my reservation.

ASSISTANT: Sure, I will help you with that. Please wait for a minute.

USER: Sure.

ASSISTANT: I am sorry to say that there is no reservation found.

USER: That's ok. Thank you.

ASSISTANT: Thank you for contacting us.