You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How Can I help you?

USER: I want to change an existing reservation. Could you please help me to change reservation?

ASSISTANT: Sure,may I know your name for changing reservation.

USER: Sure, my name is Matthew Williams.

ASSISTANT: OK,please wait a moment.

USER: Sure.

ASSISTANT: Sorry Matthew Williams, there is no reservation on your name.

USER: I want travel from DC-IAD to NC-CLTT. Travel dates are 12/26 and 12/28.

ASSISTANT: As per your requested details there is a flight matched. Shall I proceed?

USER: OK fine, you can book my ticket.

ASSISTANT: OK. Your flight ticket is booked.

USER: Thank you for helping me.

ASSISTANT: Your welcome.