You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I assist you?

USER: I want to change my existing reservation. Can you help me in that?

ASSISTANT: Sure, may I know your name?

USER: David Hall.

ASSISTANT: Ok, please wait a minute.

USER: Sure.

ASSISTANT: Sorry to say that there is no reservation found on your name.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you.