You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I serve you?

USER: As my uncle's surgery got preponed, I need attend the hospital in early dates. Can you change my existing reservation?

ASSISTANT: Sure, may I know your name?

USER: Sure, my name is Charles Clark.

ASSISTANT: OK, please wait for a while, I will check and get back to you.

USER: OK.

ASSISTANT: Thank you for waiting, unfortunately there is no reservation found on your name.

USER: OK, thank you.

ASSISTANT: Thank you for reaching us.