You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Joseph Nelson.

ASSISTANT: How may I help you?

USER: Due to sudden change in my plan, I would like to change my existing reservation. Can you help me in changing my reservation?

ASSISTANT: Sure, please wait a moment.

USER: Sure.

ASSISTANT: Nelson, there is no reservation has been found on your name in our database.

USER: Ok, that's fine. Anyways, thank you for the information.

ASSISTANT: Thank you for approaching us.

USER: Welcome.