You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. May I know your good name?

USER: I am Katherine Clark, actually I want to change an existing reservation can you help me?

ASSISTANT: Sure Clark, I will help you out. Please wait for a while.

USER: OK, sure.

ASSISTANT: Sorry, there is no previous reservation matching with your name to change.

USER: OK, thank you.

ASSISTANT: Thank you.