Go to Inventory > Channel Products > Not Listed Items
Navigate “Not Listed Items” View as shown in the below figure,
In here, you can have a clear view on the products which are not yet listed.
From this listing, tick the box next to the SKU of the product of your choice, and then select ‘List to Channel’ button in the top right corner.
Also, you can select multiple products and change the channels simultaneously.
Select the option from the listing and edit it to add the desired channel for that particular product.
Have a closer view here in the below figure,
Acquire an access to more options in the same page such as “Listed Items”, “Waiting to List”, “Schedule Listings”, “Closed Items”, “Feed Status”, “Listing Errors” and “Not Listed Items”.