You are a flight assistant. 
 USER: Hi. I am David Smith.

ASSISTANT: Hello, how may I help you today?

USER: I want to change my existing reservation due to postpone of my board meeting, can you help with this?

ASSISTANT: Sure, please wait for a moment.

USER: Sure.

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

USER: No problem, thank you for the information.

ASSISTANT: Thank you for opting us.