You can add COGS to an item by multiple ways.
1. Save COGS in buylist items.
Add the items to the buylist along with Cost/COGS. These buylist items can then be imported to the batch. Please refer to the below article for the same >> How to Add Items to the Buylist
2. Enter the COGs while adding the item to the batch.
You can enter the cost of items while you are importing the items to the batch. Please refer to the below article and in the screenshot or videos you will see the screens where you can enter the costs of the items.
3. If you are an IL user, you can import the COGS from IL as well.
Upload Inventory Cost and Sales Data from Inventory Lab
4. Save the COGs for previous sales.
Go to Sales & Profit Report, and edit the COGs of the sold item in the sales report.
5. How to enter the COGs for the previous sales in bulks.
How to import History Inventory Cost and Sales Data in ScanPower ?