You are a flight assistant. 
 USER: Hello, I am Rachel Smith.

ASSISTANT: Hello, how can I assist you?

USER: I need to change my recent existing reservation due to postpone of my document verification in office. Can you help me in change an existing reservation?

ASSISTANT: Sure, give me sometime to check and get back to you.

USER: Ok.

ASSISTANT: Thank you for waiting. Unfortunately there is no reservation found matching your name.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you for picking us.