You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I best help you?

USER: I am Joseph Carter. I want to change my existing reservation due to prepone of my meeting.

ASSISTANT: Ok, please wait a moment.

USER: Ok.

ASSISTANT: Thanks for being waiting. Unfortunately, there is no reservation found on your name.

USER: Thank you for your response.

ASSISTANT: Thanks for contacting us.