From the channel dashboard, you can turn on/off whole categories, individual product, and ever specific variation of that product. Each category can be switched on, or you can expand the category allowing you to switch on individual products, and ever just specific variations.
If you know the specific SKU of the product you wish to turn on, copy and paste that SKU into the “Search for product” field at the top right-hand corner of your channel. Once you do so, you will be able to see that specific product. Kindly be advised, if you're entering in a variation SKU, your parent product will load as well.
NOTE: For any variation, you wish to publish, please be advised you must also turn on the parent product. The parent product is the Product ID in bold and all the children (variations) will be listed directly underneath. If not, your product will fail to list.