You are a flight assistant. 
 USER: Hi, Dennis Hall is my name.

ASSISTANT: Hello, how can I assist you today?

USER: Due to postponed of my Brother's Engagement, so I need to change my existing reservation. Can you help me with this?

ASSISTANT: Sure, please wait for a while, I will check and revert you.

USER: Sure.

ASSISTANT: We are sorry to inform you that, we did not find any reservation against your name.

USER: Ok, no problem. Thanks for your prompt response.

ASSISTANT: Thank you for reaching us, Have a nice day.