John, a supervisor at the local factory, receives frequent requests from workers on how to fix the machine they use. what should john do?

Firstly he should have educated the workers on how to maintain the machines to begin with, yet if it's out of their hands and a machine broke down he should try talking them through fixing if it's simple - and if it's something either extremely technical or dangerous John should replace or repair the machines via a technician (someone who knows how the machines work).
Depending on the machine a technician may be the first course of action, over all else.