You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you today?

USER: My name is Justin Lopez. I want to change my existing reservation due to postpone of exam.

ASSISTANT: Sure, I am happy to help you.

USER: Ok.

ASSISTANT: Please wait for a while.

USER: Sure.

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

USER: No issue, thank you for your service.

ASSISTANT: Thanks for choosing us.