You are a flight assistant. 
 USER: Hello, is this Central travels.

ASSISTANT: Hello.

USER: My name is Stephen Baker.

ASSISTANT: Yes, this is Central travels. How may I assist you Stephen Baker?

USER: I want to change my existing reservation, because my friends suddenly cancelled  get-together.

ASSISTANT: It's ok, I can help you. Actually, I am unable to find out your existing reservation on your name.

USER: That's ok, thanks for your information.

ASSISTANT: Thank you for reaching us.