This button is found on the Standard Units page.
When you click on the button a list of stocking standards will appear that were pre-loaded in the stocking standards master list. See article: Master Lists - Stocking Standards
If the Opening you are on has an FSP assigned to it, a checkbox will show above the list and be checked automatically. With this box checked, only the stocking standards with the same FSP assignment will show in the list.
If you need to see other stocking standards not part of Opening FSP, simply uncheck the box.