You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you?

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

ASSISTANT: Sure, We are here to help you. May I know your name?

USER: Myself William Clark.

ASSISTANT: Give me a minute.

USER: Ok.

ASSISTANT:  Thank you for waiting, but I am sorry to say that, there is no active reservation found with your name in our database to change it.

USER: Not an issue. Thank you.

ASSISTANT: Thank you for reaching us.