To add products to the recommended section in the top menu, select the item "Products / Featured Products" and click on the "cross".
In the window that opens, start typing the name of the product. From the list that appears, select the desired product.
You can add a date to which the recommended product will be displayed on the main page or leave it unchanged (the time limit is unlimited).
Here's what the "Featured products" looks like on the main page: