You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I aid you?

USER: I would like to change my existing reservation, can you help me in that?

ASSISTANT: May I know your name?

USER: Sure, myself Charles Perez.

ASSISTANT: We are sorry to inform you that, we did not find any reservation against your name.

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

ASSISTANT: Thank you.