You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am Donna Nelson. I would like to change my existing reservation. Could you please help out?

ASSISTANT: Sure, please wait for a while.

USER: Sure, please take your time.

ASSISTANT: Sorry, there is no reservation is found by your name. Thank you and have a nice day.

USER: Ok, no problem. Thank you for the information.