Frequently Bought Together
This feature is for products that you can recommend to the bought along with the main product (simple product type, not variable).
Only simple products and product variations can be added as accessories.
To use this feature simply go to the Dashboard >> Products >> edit a product or create a new one then scroll down to the “Product data” section if the product is a simple product you will see this “Bought Together” option as you see below.
As you can see in the above image you can add products to it. Then check back this product after clearing the browser cache. Make sure that you have set the element of the “Bought Together” in the Single Product Builder as you can see in the below image