You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Charles Martinez.

ASSISTANT: How can I help you?

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

ASSISTANT: Sure, I will help you to change your reservation.

USER: Thank you.

ASSISTANT: Please allow me a moment.

USER: Sure.

ASSISTANT: Sorry, no reservation found on your name to cancel your reservation.

USER: Thank you.

ASSISTANT: Welcome, have a nice day. Thank you for choosing us.