You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you today?

USER: I am Charles Carter. I want to change my existing reservation. Can you please help me with this?

ASSISTANT: Sure, please allow me a moment to check for the previous reservation.

USER: Sure.

ASSISTANT: Charles Carter, there is no reservation found under your name.

USER: Ok, no problem. Thank you for checking.

ASSISTANT: You are welcome. Thank you for contacting us.