You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I serve you?

USER: Is it possible to change me existing reservation which I have done earlier?

ASSISTANT: Sure, I help you in getting this issue resolved and see that your flight reservation has been changed. May I know your name please?

USER: My name is Anthony Miller.

ASSISTANT: Wait for a moment please.

USER: Sure.

ASSISTANT: Thanks for your patience. But I am sorry to inform you that I could not find your flight reservation to change it.

USER: No problem, thank you for your time.

ASSISTANT: Thank you.