You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you today?

USER: I am Joseph Moore. Please help me in changing my existing reservation, as my exam scheduled has been postponed. Please help me in changing?

ASSISTANT: Ok, please wait a moment.

USER: Ok.

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

USER: Ok, no issues.

ASSISTANT: Thank you for choosing us.

USER: Thanks for your service.