You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I need to change my existing reservation.Can you help me in changing reservation?

ASSISTANT: Sure, I am here to help you. To change an existing reservation, I need to know your name?

USER: Dorothy Johnson is my name.

ASSISTANT: OK, please wait for a moment.

USER: OK.

ASSISTANT: Thanks for waiting. Sorry there are no reservation found on your name.

USER: OK, thanks.

ASSISTANT: Thank you, have a nice day.