You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you today?

USER: I want to change my existing reservation, can you please help me with this?

ASSISTANT: Sure, may I know your name to check for the previous reservation?

USER: I am Dorothy White.

ASSISTANT: Please allow me a moment.

USER: Sure.

ASSISTANT: There is no flight available at your request.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you for contacting us.