You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you?

USER: Helen Lewis here. I need to change my existing reservation as my plan to go for an historical tour got postponed. Can you please check if my reservation is active or not? If it is active, please change it.

ASSISTANT: Sure, give me a minute.

USER: Ok, take your own time.

ASSISTANT: Sorry, there is no reservation found under your name.

USER: Ok, not a problem. Anyways, thank you.

ASSISTANT: Thank you for opting us.