You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you today?

USER: Could you help me in changing the existing reservation?

ASSISTANT: Sure. Let me know your good name please.

USER: Yes, my name is Gary lee.

ASSISTANT: Sorry Gary, no reservation found under your name. Thank you for reaching us.

USER: OK, thank you.

ASSISTANT: Have a good day.