You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may i abet you?

USER: I am Rebecca Roberts. 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 wait a minute.

USER: Ok.

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

USER: It's ok, thank you.

ASSISTANT: Most welcome.