You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I assist you today?

USER: I want to change an existing reservation due to sudden change in trip. Can you help me?

ASSISTANT: Sure, please wait for a moment.

USER: Ok.

ASSISTANT: May I know your good name?

USER: I am Thomas Miller.

ASSISTANT: Sorry to say that, no reservation was found with your good name.

USER: OK. Thank you.

ASSISTANT: Thank you for opting us.