You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, could you please tell us for what help you approached us?

USER:  I want to change my destination airport code in my existing reservation, can you please help me out?

ASSISTANT: Ok, could I have your name please?

USER: My name is John Martin.

ASSISTANT: Ok, please allow me a moment.

USER: Sure, take your time.

ASSISTANT: Sorry, there is no reservation with your name in our portal to make changes further.

USER: That's ok, thank you for checking.

ASSISTANT:  You are welcome, have a great day.