How can I fix my rear wiper, mitsubishi, magna?

My son forced the rear wiper around the wrong way now it is free moving, The motor still makes a sound when the wiper is turned on but the wiper does not work. This is the 2nd time this has happened and was fixed by a mechanic in under a minute, i just don't want to pay to get it fixed if it's a simple job we can do at home. Thanks for listening.