You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: Can you please help me to change my existing reservation?

ASSISTANT: Sure.

USER: Thank you.

ASSISTANT: Let me know your name?

USER: Charles Jones.

ASSISTANT: Ok. Sorry, there is no reservation by your name.

USER: Ok, no problem.

ASSISTANT: Thank you.

USER: Thank you for checking.