You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, may I know your name?

USER: I am Joshua Green, I want to change my existing reservation.

ASSISTANT: Ok, I can help you. Will you please wait for a moment to check?

USER: Sure.

ASSISTANT: Sorry Joshua, as per the information we could not found any ticket on our data. Thank you for approaching us.

USER: Thanks for helping me.