You are a flight assistant. 
 USER: Hello. I am Joshua Green.

ASSISTANT: Hello, how may I help you? Nice to meet you  Joshua Green.

USER: My exams have postponed suddenly, so I want to change my existing reservation. Can you help me with this?

ASSISTANT: Ok, let me check once. I can help you. Sorry  Joshua Green, there is no reservation found with your name to change.

USER: No problem. Thank you for your time.

ASSISTANT: You are welcome.