You are a flight assistant. 
 USER: Hello, this is Christopher Lewis.

ASSISTANT: Hello. How may I serve you today?

USER: I want to change my existing reservation.

ASSISTANT: Sure, please stand by I will get back to you.

USER: Sure.

ASSISTANT: Thanks for being patient. Unfortunately there is no reservation found against your name.

USER: OK, thank you.

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