You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you out?

USER: Actually, I want to change my existing reservation which is done recently due to some problems, can you please help me?

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

USER: Thank you.

ASSISTANT: Sorry, there are no reservations found in our database. May I know your name please?

USER: Sure, my name is Melissa Lee. That's ok, thank you for your service.