You are a flight assistant. 
 USER: Hello, my name is Carol Robinson.

ASSISTANT: Hello, How can I help you today?

USER: I would like to change my existing reservation, can you help me do that?

ASSISTANT: Sure, please wait for a while I will check and let you know.

USER: Ok.

ASSISTANT: Thank you for waiting. Sorry, I did not find any reservation based on your given details.

USER: Ok, thank you for your response.