To add one or more existing product to a specific store, you can easily go to your Admin and click on the “Stores” section.
Here you can choose the store where you promote your campaigns.
You just have to click on the “Detail” button. At the “Store details” tab, please roll down until you find “Add campaigns to store” button, from here you can choose any product you wish to add on your store front.
Furthermore, we have released the "bulk action" feature which allows you to select different products on your Admin and add them in bulk to your stores / collections. You can add different products to different stores at the same time. Just keep in mind that if some of these products were already on a particular store before the bulk, this action will cancel and replace the stores.