You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Helen Martinez.

ASSISTANT: How may I assist you now?

USER: I would like to change my existing reservation due to postpone of my exams. Could you please help me?

ASSISTANT: Helen Martinez, please allow me to check with your previous booking.

USER: Sure.

ASSISTANT: Sorry to say, there are no flights available for your journey.

USER: No worries, thank you for the information.

ASSISTANT: Thank you for choosing our services.