You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Sandra Miller.

ASSISTANT: How can I help you?

USER: I want to change my existing reservation due to postpone of my client meeting, can you please help me in that?

ASSISTANT: Sure, I am glad to help you. Please wait for a while.

USER: Sure.

ASSISTANT: Sorry, there are no reservation found on your name.

USER: No problem, thank you.

ASSISTANT: Thank you for opting us, have a nice day.