The original stroke (and its path) has been converted to outlines, and so has been lost in the process. There's no way to get it back. Converting to outlines is destructive and not reversible.
You could do Break Apart to break the compound path, ungroup it, then delete one of the paths, then apply a stroke and fill, but the stroke would now be in a slightly different position from the original, being slightly outset/inset.
You could try to outset/inset the path slightly to try to bring it back to the original path position, then do Object to Path.
You also could do Break Apart, ungroup, select both pieces, and then use the Interpolate extension to try to recreate the original path in the middle, which has been lost. Then do Object to Path, and delete the extraneous paths.
However, to be honest, most of these solutions are quite tedious. Personally, since the graphic is very simple anyway, I'd just grab the pen tool and redraw it, or draw a bunch of circles and unite the ones in the cloud shape.