You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello. How can I help you?

USER: I am Charles miller . I like to change my existing reservation .

ASSISTANT: Sure Charles, give me a minute.

USER: Sure.

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

USER: OK .

ASSISTANT: Thank you.

USER: Thank you.

ASSISTANT: Have a great day.