You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello, how can I assist you?

USER: I need to change my existing reservation.

ASSISTANT: Sure, may I know your good name please?

USER: I am Dorothy Smith.

ASSISTANT: Thanks for giving your name, please wait for a while I will check the availability and revert you.

USER: OK,.

ASSISTANT: Thank you for waiting, sorry to inform you that there is no reservation found on your user name.

USER: OK, Thank you for your help.

ASSISTANT: Thank you for contacting us, have a great day.