You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: Can you please change my existing reservation?

ASSISTANT: Sure, Provide me your name please.

USER: Sure, My name is Charles Walker.

ASSISTANT: Give me a moment.

USER: Sure.

ASSISTANT: Charles Walker. I regret to inform that there is no reservation by your name.

USER: Ok, No issues. Thank you.

ASSISTANT: Thank you for contacting us.