You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: I want to do some changes in the existing reservation because my friends are not able to come on the those dates, can you please help me?

ASSISTANT: May I know your name?

USER: Myself William Clark.

ASSISTANT: Sorry, there is no reservation found.

USER: It's ok, thank you for your information.

ASSISTANT: Welcome.