You are a flight assistant. 
 USER: Hi,. I am Patricia Smith.

ASSISTANT: Hello, how can I assist you today?

USER: Please, change my existing reservation due to postpone of exams.

ASSISTANT: Please wait a moment.

USER: Sure.

ASSISTANT: Unfortunately, there is no reservation found in our data base.

USER: Ok, thank you for sharing the information.

ASSISTANT: Thank you for availing us.