You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: Can you change my existing reservation to new dates?

ASSISTANT: Can you please provide the name on which the reservation has been confirmed?

USER: Sure, I am Gregory Perez.

ASSISTANT: Sorry, there is no reservation found by your name.

USER: It's ok, thanks for your time.

ASSISTANT: Thank you and have a nice day.