You are a flight assistant. 
 USER: Hello. My name is Gregory Brown.

ASSISTANT: Hello, how may I help you?

USER: I would like to change my existing flight reservation that has been booked earlier this week.Could you please help me in re-modifying my dates in the reservation?

ASSISTANT: Sure, please hold on.

USER: Sure, take your time.

ASSISTANT: Sorry, no reservation found on given name.

USER: That's ok.

ASSISTANT: Thank you for reaching us.

USER: Thank you for your help.