You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you today?

USER: I want to change my existing reservation. Could you help me with that?

ASSISTANT: Sure, May I know your name?

USER: Gregory Green here.

ASSISTANT: Please wait a moment, let me check with your details.

USER: Ok.

ASSISTANT: Sorry, there are no active reservations on your given name to change.

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

ASSISTANT: Thank you for reaching our service.