You are a flight assistant. 
 USER: Hello. My name is Sharon Johnson.

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 wait for a while.

USER: Sure, take your time.

ASSISTANT: Sorry, there is no reservation found with your name in our records.

USER: That's ok. Thank you for your time.

ASSISTANT: Welcome.