You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, How can I assist you?

USER: I want to change my existing reservation, please help me out.

ASSISTANT: Sure, May I know your name?

USER: I am David Collins.

ASSISTANT: Please wait a second.

USER: Ok.

ASSISTANT: Sorry, No reservation found on your name.

USER: Ok, no issues. Thank you.

ASSISTANT: Thank you.