In other words...
If I'm Germany (or some other belligerent power) and I've occupied a city with a bunch of factories, how do I get those factories do actually produce stuff I want? Wouldn't factories need to be re-tooled? Where would they find skilled/unskilled laborers? Etc. Or were such factories actually rarely if ever used?
I mention the World Wars because they seem like the most obvious examples. But I am happy to learn about any other relevant historic (or even contemporary) examples.
It is well-documented that the Nazis (WW2) took over captured weapons factories and used them to turn out lots of weapons for use by the Wehrmacht. Examples include the FN-High Power, the Polish Radom, the FN M1922, the Norwegian Colt .45, and there are lots more. The Czech VZ 24 and VZ 33 rifles were produced on captured equipment by the Germans. For reference, see any edition of "Small Arms of the World" by Smith. Much of the labor (skilled and otherwise) was essentially slave labor from the conquered population.