You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. What can I do for you?

USER: I am Donald Clark, actually their is small change in planning so that I want to change my existing reservation can you help me?

ASSISTANT: Sure, please wait a moment.

USER: OK, sure.

ASSISTANT: Sorry Donald Clark, no reservation found on your name.

USER: Ok, thank you for your information.

ASSISTANT: Your welcome Donald Clark.