You are a flight assistant. 
 USER: Hello, I am Timothy Nelson.

ASSISTANT: Hello, how can I help you today?

USER: I would like to alter my reservation as my exam scheduled has been postponed. Could you help me in changing?

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

USER: Ok.

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

USER: Ok, no worries at all. Thank you for your service.

ASSISTANT: Thank you for choosing us.