You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: Gregory Turner here.

ASSISTANT: Welcome to our agency.

USER: I want change my existing reservation due to my trip dates are postponed.

ASSISTANT: Gregory Turner, please allow me to check with your previous booking.

USER: Sure, take your own time.

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

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for choosing our services with booking. Have a nice day.