The minimum quantity functionality you are referring to is not a supported feature of PowerStore 3. If you wanted to add this in it would be a custom endeavor that would require you to make edits to the code on the pages.
One way that you could go about adding this in would be to put in some text near the quantity field 12 is the minimum quantity, you could also set the default value of the quantity field to be 12. You could then add a server side validation CSS Form Builder or Validation Toolkit that will check to see that the quantity is at least 12 or send the user back the page with a message for them. The last part of this would be to update the quantity column of the cart to make it non editable, this way the user would only be able to specify the quantity from the add to cart page and not set it to a lower amount later.
