You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello,. How can I assist you today?

USER: I need to change my existing reservation. Can you please change it?

ASSISTANT: Sure,. May I know your good name please?

USER: David Taylor is my name.

ASSISTANT: Ok, please wait for a while I will the check availability and revert you.

USER: Sure.

ASSISTANT: Sorry to inform you no flight reservation found in your given name.

USER: No problem, thanks for your information.

ASSISTANT: Thank you for opting us. Have a nice day.