The "ess_grid" file is located inside the "extra" folder of the full downloadable theme folder from ThemeForest. To import the file please follow these steps:
1. Please navigate to Ess. Grid -> Import/Export
2. Click on the "Import" panel
3. Upload the "ess_grid.json" file
4. Click the small "Read File" button
5. Click "Import Selected Data" button (please do not click the full demo data button)
The essential-grid file has been uploaded successfully. If the grid is not showing up on your website please follow the steps in this article.