I'm not sure what you mean by 'open'. if you mean just open the drawer, use the no sale button. If you mean it is showing a CLOSED error, you need to log on with your id code and the clerk button. If you need a manual, one of the users has it here:
http://the-checkout-tech.com/manuals/cashregisters/Samsung_ER-4615_operating_programming_manual.html
Registerman, October 2013