As long as you didn’t delete the “parent” part, (what you described as the top level label) but only deleted the “children” parts, (the individual pieces) you should be able to reselect the parent part and move/copy what’s left of the prefab.
You can even add parts to a parent category too, if you want. To do that, select the piece(s), right-click them in the content browser, and click “attach.” It will then display all available actors; type in the search bar whatever parent you want to attach it to, and click on it.
That should add the original piece to the parent you selected.