You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, how can I help you?

USER: I am William Miller. Due to some reason I want to change my existing reservation. Will you help me in changing my reservation?

ASSISTANT: Sure, please wait for a moment.

USER: OK.

ASSISTANT: Sorry, no reservation found with your name.

USER: OK,not an issue.

ASSISTANT: Thanks for choosing us.

USER: Thank you for sharing information.