You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, may I know your name please?

USER: My name is David Roberts.

ASSISTANT: How may I assist you today?

USER: I want to change my reservation.

ASSISTANT: Sure David, please wait for a minute.

USER: OK.

ASSISTANT: I am really sorry, I cannot find any reservation with your name.

USER: Thanks for your help.

ASSISTANT: It was my pleasure, thank you so much for contacting us.