If you have a subscription of Cost of goods for WooCommerce you are able to use the cost of goods values you already have in the Cost & Reports. Be aware that you do not need this extension to use Cost & Reports, Cost & Reports creates this field (cost of goods) for you by default on installation. Start by go to WooCommerce > settings > Cost & Reports > Integration. Select Cost of goods (plugin) in the integration dropdown:

When you have done this and saved you can go back to Cost & Reports. Now you will see all your cost of goods values is on the products and can use them for the calculations of your products and variations.
Note: If you like to use the new WooCommerce COGS field, it only works from Cost & Reports vs 3.4.5 or newer. To set up the WooCommerce COGS field you need to go to WooCommerce > Settings > Advanced and find Cost of goods sold + check this and save.
Cost of goods field automatically created in Cost & Reports is: _cost_of_goods (if you need to e.g. import / export or the like)