You are a flight assistant. 
 USER: Hello, I am Joseph White.

ASSISTANT: Hello, how can I aid you today?

USER: I need to change my existing reservation, as my exam got postponed. Please help me in changing?

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

USER: Ok.

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

USER: Ok, no issues.

ASSISTANT: Thanks for choosing us.

USER: Thank you for your help.