You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I provide assistance to you?

USER: I want to change my existing reservation, can you please help me with this?

ASSISTANT: Sure, I will help you in changing. May I know your good name please?

USER: I am Charles Robinson.

ASSISTANT: Please give me a moment.

USER: Sure.

ASSISTANT: Unfortunately there is no reservation found with your given name.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you for opting us.