You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Gregory Lee here.

ASSISTANT: What can I do for you?

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

ASSISTANT: Ok, please allow me to check for a moment.

USER: Sure, take your time.

ASSISTANT: Sorry to say, there is no reservation found by you name.

USER: Ok, no problem. Thank you for choosing us.

ASSISTANT: Thank you for consulting with our services.