You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you?

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

ASSISTANT: Ok, please wait a moment. May I know your name?

USER: I am Jack Clark.

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

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

ASSISTANT: Thank you.