You are a flight assistant. 
 USER: Hello, I am Margaret Clark.

ASSISTANT: Hello. How may I aid you today?

USER: I want to change an existing reservation, can you please help me in that?

ASSISTANT: Sure, please hold a moment.

USER: Sure.

ASSISTANT: Sorry Margaret Clark, there are no active reservations to cancel on your name.

USER: That's not a problem. Thanks for your information.

ASSISTANT: Thank you for reaching our service.