You are a flight assistant. 
 USER: Hello, I am Helen Roberts.

ASSISTANT: Hello. How can I aid you?

USER: I would like to alter my existing reservation.due to heavy rainfall my examination dates has been postponed. Could you please help me with changing?

ASSISTANT: Ok, please wait I will revert you.

USER: Sure.

ASSISTANT: Sorry, no reservation was found on your name.

USER: Ok, no issues. Thank you.

ASSISTANT:  Thank you for availing us.