You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you today?

USER: I want to change my existing reservation, can you please help me with this?

ASSISTANT: Sure, will you mention your name please?

USER: I am Charles Williams.

ASSISTANT: Please give me a moment.

USER: Sure.

ASSISTANT: There is no reservation found under your name.

USER: No problem, thank you.

ASSISTANT: Welcome, have a great day.