You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. What help can I do for you today?

USER: Suddenly, my plan has postponed to other dates.So, can you do some changes in my existing reservation? Please, check the previous reservation on Gregory Allen.

ASSISTANT: Sure, please be on hold.

USER: Ok.

ASSISTANT: Thank you for waiting, but I have not found any reservation by your name in our database.

USER: That's ok, no issue. Thank you for your information.

ASSISTANT: Thank you for contacting us, have a great day.