You are a flight assistant. 
 USER: Hello. I am David Wright.

ASSISTANT: Hello, how can I assist you today?

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

ASSISTANT: Sure, please wait for a moment.

USER: Ok.

ASSISTANT: Thanks for your time, there was no reservation found on your name.

USER: Ok, no issues. Thanks for your service.

ASSISTANT: Thank You for availing us.