You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Karen Evans.

ASSISTANT: How may I help you?

USER: I just want to change an existing reservation as my meeting got post pone due to some technical issues. Can you help me with it please?

ASSISTANT: Ok, please allow me to check with your previous booking. Sorry to say, there is no active  reservation found by your name in our data base.

USER: That's ok, thank you for the response.

ASSISTANT: Have a nice day.