You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello,.

USER: I am Williams Smith.

ASSISTANT: Ok.

USER: I need to change my existing reservation, Can you please help me with that?

ASSISTANT: Sure, I will help you with that.

USER: Thank you.

ASSISTANT: Please wait, let me check your reservation status.

USER: Sure.

ASSISTANT: Thanks for waiting. Sorry Williams, there is no active reservation on your name to change it.

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Thanks for your presence.