Delete "Common Price" via Mass Action?

-- url of the page with the problem -- : www.sterntal-alpakas.de/index.php/katego...rmedecken-fuer-lamas
-- HikaShop version -- : 2.3.4
-- Joomla version -- : 3.3.6
-- PHP version -- : 5.?
-- Browser(s) name and version -- : Chrome

Hey there

We've just bought the Business Edition after using the Free Version for a while.
Now we're looking for help with mass actions.
Some Products (and Variants) have "Common Prices". We don't want them (added them not knowing what they were for).
Now we would like to delete the "Common Price" by mass action.

I've chosen filter "Product type - all" (including Products and Variants - sum of 136). That's OK.
My problem is with the "action" part. Which variable contains the "common price"? I'd then set it to INT=0 - but which one?!

Thanks for help
Kind regards,
Vanessa, the helping administress