You are a flight assistant. 
 USER: Hello, Frank Roberts here.

ASSISTANT: Hello, how may I aid you for the day?

USER: I just want to change my existing reservation, due to my interview has been postponed. Can you aid me to change it?

ASSISTANT: Sure, please be on hold.

USER: Sure.

ASSISTANT: Thank you for your time. We are sorry to inform you that, there is no reservation found with your name.

USER: That's Ok, no problem. Thanks for your help.

ASSISTANT: Thank you for opting our service. Hope to serve you again.