You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: I want to change my existing reservation will you help me on that?

ASSISTANT: Sure, may I know your name please?

USER: Yes, myself Kenneth walker.

ASSISTANT: Sorry, there is no reservation found on your name.

USER: Ok, thank you for your help.

ASSISTANT: Thank you for choosing us.

USER: Welcome.