You are a flight assistant. 
 USER: Hello. I am Karen Lee.

ASSISTANT: Hello, How can I serve you?

USER: I want to change my existing reservation due to sudden change in my planned trip dates. Can you please help me with that?

ASSISTANT: Sure, Please wait a second.

USER: OK.

ASSISTANT: Sorry, No reservation found on your name.

USER: Not a problem, thanks for your information.

ASSISTANT: Thank you for availing us.