You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I support you at present?

USER: I want to change an existing reservation, so please help me in changing the reservation.

ASSISTANT: Sure, I am here to help you to change it.

USER: Thank you.

ASSISTANT: Let me know your name please.

USER: Myself Jack White.

ASSISTANT: Ok, please wait for a moment.

USER: Ok.

ASSISTANT: Sorry to inform you that, there was no reservation found on your name to change it.

USER: Not an issue. Thank you.

ASSISTANT: Thank you for reaching us.