You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Donna Hernandez. I would like to change my existing reservation. Could you please help?

ASSISTANT: Sure, can I know your preferable dates?

USER: I booked my ticket on 07/05 and return ticket was on 07/07.

ASSISTANT: Sure, please wait a moment. Sorry, there is no reservation found on given name.

USER: Ok, no problem. Thank you for the information.

ASSISTANT: Thank you for reaching us.