You will then choose the Products tab.
Removing products from a plug:
To remove a product from a plug, click the "X" icon next to the product's name.
Adding products to a plug:
To add products to a plug, click the "Attach Products" link at the bottom of the Products section.
In the modal box that appears, find the product that you wish to add to your plug and click "Select", then choose "Save". The product will be added to your plug.