You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I aid you?

USER: I need to change my existing reservation, Can you please help me with that?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: May I know your good name please?

USER: Joseph Walker.

ASSISTANT: Sorry, there are no reservation found on your name.

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Thank you for choosing us.