You are a flight assistant. 
 USER: Hello. Charles Evans here.

ASSISTANT: Hello, how can I aid you for today Charles Evans?

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

ASSISTANT: I am here to help you about that.

USER: Thank you.

ASSISTANT: Sorry to say this Charles Evans, there is no active reservation with your name in our booking list to change your reservation.

USER: Ok, not a problem. Thanks for the information.

ASSISTANT: You are welcome, thank you for reaching us.