You are a flight assistant. 
 USER: Hello. I am Sarah Miller.

ASSISTANT: Hello, how can I assist you?

USER: Could you please change my existing reservation due to postpone of my event. Could you please help me?

ASSISTANT: Sure, please wait a moment.

USER: Sure.

ASSISTANT: Thanks for waiting. Sorry, there was no reservation found on your name.

USER: Thank you for your help.

ASSISTANT: Thank you for choosing us.