You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, How can I best serve you today?

USER:  I need to change my existing reservation as my exams got postponed, Can you please help me with that?

ASSISTANT: Sure, I am here to help you with that, can I know your good name to proceed further?

USER: John Nelson here.

ASSISTANT:  I am very sorry to inform you that there is no reservation found under your name in our database.

USER: No issue, thanks for the information.

ASSISTANT: Thank you for choosing us.