You can add/remove products from a plug after you have created it at any time by visiting your Plug's infopage. In your Plugs page click the 3 dot menus on the right and choose the "View info".

Removing products from a plug:

To remove a product from a plug, click the 3 dot menus on the right and select the delete option.

Adding products to a plug:

‍

‍

‍