transfer purchase code to our new website

We have purchased “BeTheme” and activated it on our website Now we want to move to another website and move our theme there. To do so we deregistred the purchase code from, but when we are about to add it to our new website, we got the message “Purchase code already used. Please deregister purchase code and remove theme folder on:”.

Can you walk me through the process of adding our purchase code to the new website
Thank you