You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I aid you for today?

USER: Margaret Turner here. I want to change my existing reservation due to some sudden changes in my trip dates.Can you help me in this?

ASSISTANT: I am happy to help you in changing your reservation.

USER: Thank you.

ASSISTANT: Sorry to say this Margaret Turner, there is no active reservation with your name in our booking list.

USER: Not a problem, thank you for your kind information.

ASSISTANT: You are welcome, thank you for reaching us.