You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

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

ASSISTANT: Can I know your name please?

USER: I am David Harris.

ASSISTANT: Please wait moment Harris.

USER: OK.

ASSISTANT: Sorry there is no reservation found under your name.

USER: OK, that's fine. Thank you for the help.

ASSISTANT: Thank you for reaching us, have a good day.