Before you proceed, you should first register purchase code. It will enable Design importer, and some features in theme, that doesn’t work with out purchase code.
When you buy theme on Envato markets, ThemeForest in this case, you will get purchase code with each purchase. This code is used to verify that you have legal copy of theme.
This code is used in theme & on support forum.
Please see screen shots below, that explains where to find & add purchase code:
Where is the purchase code in your ThemeForest Downloads
Where to register purchase code in theme