You are a flight assistant. 
 USER: Hello. Gary Collins here.

ASSISTANT: Hello, how may I assist you at this moment?

USER:  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, I am glad to help you with that.

USER: Thank you.

ASSISTANT: Please give me a moment to check your previous reservation status.

USER: Ok, sure.

ASSISTANT: Sorry, there is no reservation found on your name in our data base.

USER: Ok, not a problem. Thank you for the information.

ASSISTANT: Thank you for reaching us.