Depending on your products, the Related Items that we calculate are similar items to the product that is being viewed. These are based on different parameters such as tags, keywords, collections, clicks, etc.
If you would like to match your products to each other and promote a specific product to each other, you can use the Cross-sell recommendation box. To select the cross-sell items to your products, go to your LimeSpot admin panel > Content > Products. Then click on the product you would like to select cross-sell items for.