You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: William Jones here. I would like to change my destination airport code, please help me in changing my existing reservation.

ASSISTANT: Sure, I am happy to assist you with that. Can you please give me a minute?

USER: Sure, take your time.

ASSISTANT: I regret to inform you that, there is no active reservation with your name in our portal to change the details.

USER: Ok, no issues. Thank you for your information.

ASSISTANT: Most welcome. Thank you for choosing us.