The driver side windshield wiper does not work. The other side works fine so I know it isn‘t the motor. What do I need to do to fix it?
That depends on what the magnet is made of. See the web pages.
either the nut on the wiper arm has loosened up and stripped out, or the linkage has broken. Both are relatively easy fixes. if it is the linkage you need to remove the black cowl and inspect to see whether it is broken or maybe has a loose bolt. good luck
Magnets are made of ferromagnetic substances. They usually lose their ferromagnetism at or above a temperature called Curie Temperature which is different for different substances. So please specify the substance.