You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I aid you?

USER: I am Margaret Hall. I want to change my existing reservation. Could you help me?

ASSISTANT: Sure, I will help you. Please wait for a while.

USER: Ok.

ASSISTANT: Sorry, there is no reservation existing on your name.

USER: That's ok, no problem. Thank you.

ASSISTANT: You are welcome, have a nice day. Thank you for opting us.