You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, what kind of service are you looking from us?

USER: Could you help me to change my existing reservation?

ASSISTANT: Sure, we will help you in that.

USER: Thank you.

ASSISTANT: May I know on whose name the ticket has been reserved formerly?

USER: Robert Green here.

ASSISTANT: Please wait a minute, I will check your reservation status and get back to you.

USER: Ok.

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

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for reaching us.