You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you?

USER: I am Helen Nelson. I want to change my existing reservation due to postpone of my client meeting, can you help me in changing reservation?

ASSISTANT: Sure, please wait a moment, I will check the reservation list.

USER: Sure.

ASSISTANT: Sorry there is no reservation on your name.

USER: No problem, thank you.

ASSISTANT: Thank you.