I've heard about a quick stock option for items in your inventory. How do I access it?

Go into any one of your shop management pages, as if you were going to change its inventory. Along with the options you'll find there (between "Edit Items" and "Edit Shop"), you'll find "Quick Stock."

The reason you have to go into a shop to do it is because Subeta allows you to have more than one shop, and they don't want to add loads and loads of options to the quick stock pages.

Ok, thanks a lot! :)