You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you?

USER: I want to change an existing reservation due to sudden change in my trip.

ASSISTANT: Sure, may I know your name?

USER: I am Alexander Lewis.

ASSISTANT: Sorry to inform you that there is no reservation on your name.

USER: No issue. Thank you.

ASSISTANT: Thank you for opting us.