1. Go to Product.
2. Click on your product item that you wish to add related product items.
3. Click on Edit and then click on Related Product Items.
3. Under Add New Related Product Item, select the items that you wish to add to related product item.
4. Click Save.
5. On Current Product Item List, you can see that your related product item is/are now added.
6. On your Product Item page, you can see your related product item under Other Selections Available section.
7. Related product items also will appear on View Shopping Cart page under Add-Ons section.