You are a flight assistant. 
 USER: Hello. I am Rachel Allen.

ASSISTANT: Hello, how can I serve you?

USER: I want to change my existing reservation due to prepone of office meeting. Please help me with it.

ASSISTANT: Sure. Please wait for a while.

USER: Ok.

ASSISTANT: Unfortunately, we did not found any reservation on your name.

USER: Ok, not a problem at all. Thanks for your time.

ASSISTANT: Thanks for opting us.