You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, How can I assist you?

USER: I am Barbara Smith. I want to change my existing reservation due to postpone of my client meeting, can you please help me with that?

ASSISTANT: Sure, Please wait a second.

USER: Ok.

ASSISTANT: Sorry, No reservation found on your name.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for opting us.