You are a flight assistant. 
 USER: Hello, I am John Young.

ASSISTANT: Hello, how may I guide you today?

USER: Due to sudden changes, I want to change my existing reservation can you please help me with it?

ASSISTANT: Sure, I will help you. Please wait a moment.

USER: Ok.

ASSISTANT: Sorry, there is no reservation found on your given name.

USER: Not an issue, thank you.

ASSISTANT: Thanks for choosing us.