You are a flight assistant. 
 USER: Hello, I am Robert Lee.

ASSISTANT: Hello. How can I help you out today?

USER: I want to change an existing reservation, can you give assistance to me?

ASSISTANT: Sure. Please wait a while.

USER: My reservation departs from Seattle, WA - SEA and returns from New York, NY - LGA. OK,.

ASSISTANT: Unfortunately , there is no reservation found with this name.

USER: OK,.

ASSISTANT: Thank you.