You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I serve you today?

USER:  I am Karen walker. I want to change my reservation due to prepone of my meeting.

ASSISTANT: Sure, we are glad to help you. Ok, please hold a minute, let me check your reservation with us.

USER: Ok.

ASSISTANT: Thanks for your valuable time, unfortunately no reservation found on your name.

USER: Ok, thank you for your response.

ASSISTANT: Thank you for approaching us, have a great day ahead.