You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, how can I useful to you?

USER: I am David Jackson. I want to change my existing reservation due to postpone of my board meeting so, can you help with this?

ASSISTANT: Sure, we are here to help you. Please wait a moment, I will check the reservation list and get back to you.

USER: Sure.

ASSISTANT: Sorry to inform you that there is no reservation found on the name David Jackson to do modification.

USER: No problem, thank you.

ASSISTANT: Thank you for reaching us.