You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I'm William Martinez here, I want to change my existing reservation. Can you please help me?

ASSISTANT: Sure, may I know your name?

USER: I have mentioned above.

ASSISTANT: Please, wait a moment let me check the previous details on your name. Ok.

USER: Sure.

ASSISTANT: Sorry, no reservation found on your name.

USER: Thank you for contacting us. Ok, no problem.

ASSISTANT: Thank you for reaching us.