Unfortunately, there's no direct way to restore the elevations set before you grouped objects, but you could use the Furniture > Elevate menu item proposed in Advanced editing plug-in to help you change back elevation faster.

Note that you should have proceeded differently in the first place to hide objects: you could have selected all the objects you wanted to hide then choose Furniture > Modify menu item to change their visibility at once. You could also create levels at the same elevation as existing ones where you would cut / paste furniture you want to hide, then make the levels with furniture not viewable while you print.