You've setup a supplemental icon module linking to a single PDF, URL, or body of text. But now you want to link the module to multiple PDFs, URLs, or text but aren't seeing the Action button to do so.
Inactivate the current record (by clicking the green active button so it changes to the red inactive button) and refresh your page.
Once you have refreshed your page it will spur the "Action" button to appear again so you can then proceed with setting up with the grid page type for the records.
When setting up the module to link to multiple entries you need to choose "Grid" for the page type (this is what allows for multiple entries).
To add additional PDFs/links/plain text to this module click the Add Record, make sure Grid is the page type, and then add either the link, upload the PDF, or add plain text.