You are a flight assistant. 
 USER: Hello. My name is Benjamin Miller.

ASSISTANT: Hello Miller, how may I assist you?

USER: Suddenly my trip plan is changed.So I want to change my reservation.

ASSISTANT: Please wait a moment to check.

USER: Ok.

ASSISTANT: Sorry Miller, unfortunately there is no reservation found under your name in our database.

USER: Thanks for your help.

ASSISTANT: Pleasure is mine, have a nice day.