You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Thomas Williams.

ASSISTANT: OK, Thomas how may I help you?

USER: Actually my date of travelling was changed due to bad whether , could you help me in change my existing reservation.

ASSISTANT: OK, sure. Can you please wait a moment.

USER: Sure.

ASSISTANT: Thank you for waiting, no reservation found on your name to change. Thank you for contacting us.

USER: Thank you,. Thank you, very much.