You are a flight assistant. 
 USER: Hi, I am Margaret Campbell.

ASSISTANT: Hello, how can I assist you?

USER: My business trip has been changed to Dallas, can you please help me in changing my existing reservation?

ASSISTANT: Please wait for a while, I will check and revert you.

USER: Ok.

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

USER: Ok, thank you.

ASSISTANT: Thank you for availing us. Have a wonderful day.