You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you today?

USER: Charles Johnson here. Due to inconvenience of my work, I want to change my reservation. Can you please help me for that?

ASSISTANT: Sure, I am here to help you.

USER: Thanks.

ASSISTANT: Sorry Charles, there is no reservation found under your name to change your reservation.

USER: Anyway, thanks for the information.

ASSISTANT: You are welcome always.