You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: William Carter here.

ASSISTANT: I am here to assist you, may I know your concern?

USER: Can you change my existing flight ticket reservation?

ASSISTANT: Ok, please wait.

USER: Sure.

ASSISTANT: Thank you for waiting.

USER: Ok.

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

USER: Ok, that is not a problem. Thanks for checking.

ASSISTANT: Thank you for connecting with our agency.