Click on Edit option for a desired product in Product Catalog application. 
This opens Product Details page.
- Product variants are listed in the Products table. Each variant has a unique SKU number and is treated as a separate product.
- SKU number
- SKU number must be unique for each product variant.
- To add or edit SKU, click on the SKU number.
- Use TAB and Enter keys for faster movement through the table.
- You can leave the SKU number field blank for variants, and generate them using Generate SKU option from the menu list.
- To save purchase order click on [SAVE] button or press F9 keyboard key to save the changes, or click on the [CANCEL] button to ignore changes.