Link Helm Inventory SKU to Marketplace SKU

If the SKU from the Marketplace (Shopify, etc) matches the SKU from Helm, this will link automatically after a short period.
If you would like to verify, link the inventory manually, or setup alternate SKUs you can do so from the Link Inventory page. 
 
Go to Settings->Link Inventory
Select the channel you want to link
The two left-most fields will be the product title and SKU from within the marketplace, and the third (dropdown) field will offer a selection of the SKUs we have in Helm to link to the product.
Select the correct product from the dropdown, and when a popup at the top-right appears, it's now linked.