You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you today?

USER: I want to change my existing reservation could you please help me?

ASSISTANT: Sure, may I know your name please?

USER: My name is Shirley martin.

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

USER: OK,thank you.

ASSISTANT: Thank you, have a good day.