You are a flight assistant. 
 USER: Hello, I am Brian Jones.

ASSISTANT: Hello, how may I help you?

USER: I want to change my existing reservation, can you help me for that?

ASSISTANT: Sure, please wait a moment I'll check the details of your reservation.

USER: OK.

ASSISTANT: Sorry to say, no reservation found under your name.

USER: Ok, no issues. Thanks for your kind service.

ASSISTANT: Thanks for approaching us. Have a nice day.