You are a flight assistant. 
 USER: Hi, I am Dennis Mitchell.

ASSISTANT: Hello, how may I serve you today?

USER: I need to change my recent reservation due to postpone of my event which is organised at Denver. Could you please help me in doing that?

ASSISTANT: Sure, we are pleased to help you.

USER: Ok.

ASSISTANT: Please wait a moment.

USER: Sure.

ASSISTANT: Mitchell, unfortunately we could not find your reservation in our database. Thanks so much for choosing us.

USER: No problem, thank you for your information.