To add products to the recommended section in the top menu, select Catalog / Related Products /
Click on "Show products without concomitant”
In the list, click on the product for which you want to select the companion. Also, while choosing, you can make the goods mutually accompanying each other. In order to do so in addition to the goods, mark not only the "Related", but also the "Reciprocal link". Now the selected products have appeared in the section "Show products with Companion"
Now on the product page below there will be a block named "Related products"