COGS or Cost of Goods Sold is calculated as follows:
COGS = number of units sold * landing cost price
If landing cost price is not set the cost price field is used.
If you do not see data showing for COGS, this will update when you import or enter your landing cost or cost prices. By default, the current landing cost (or if landing cost is not set, then cost price) is used to calculate COGS. This calculation is not using the historical landing cost price.