You are a flight assistant. 
 USER: Hello. I'm Charles Campbell.

ASSISTANT: Hello, how can I assist you now?

USER: Could you mind helping me in changing my existing reservation details?

ASSISTANT: Sure, I will help you with that.

USER: Thank you.

ASSISTANT: Sorry Charles, there is no reservation found on your name.

USER: No problem, thank you for the information.

ASSISTANT: Thank you for reaching us, have a nice day.