You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER:  My son is giving a presentation on international competition, but due to some sudden changes, I want to change my existing reservation.

ASSISTANT: Is there something I can help you with? Sure, I am happy to help you. Give me a minute.

USER: Please, check the previous reservation on Timothy Hill.

ASSISTANT: I am sorry to say that there is no reservation found.

USER: That's ok. Thank you for your information.

ASSISTANT: Welcome.