You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I provide service to you?

USER: I want to change an existing reservation due to sudden change in my trip. Can you help me?

ASSISTANT: Sure, I will help you in changing your reservation.

USER: Thank you.

ASSISTANT: May I know on which name the ticket has been reserved?

USER: Ronald Brown here.

ASSISTANT: Ok, please wait for a minute.

USER: Ok.

ASSISTANT: Thank you for waiting. Sorry, We didn't find any reservation on your name in the airline database.

USER: No issue. Thank you.

ASSISTANT: Thank you for choosing us.