You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you today?

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

ASSISTANT: Sure, may I know your name?

USER: I am Mark Williams.

ASSISTANT: Ok, please wait a moment.

USER: OK.

ASSISTANT: Sorry, to inform no reservation found with your name.

USER: Ok, thanks for your great response.

ASSISTANT: Thanks for choosing us, have a good day.