Rear wiper blade not working? on 2004 Kia Spectra

When I push the button for rear wiper, the engine connects and it trys to move but no success. If the threads are stripped do I need to replace the whole engine?
Thank you

Asked by for the 2004 Kia Spectra
Tighten the nut at the base of the wiper arm, it under the plastic cover. Be sure wiper and wiper motor are parked! Turn key on, turn rear wiper on, turn wiper back to off then turn key off. Now make sure wiper is in it's normal off or parked position! Tighten the nut.
Just so I am clear do you mean the plastic hub on the outside of car, not on the inside where the engine is?
At the bottom of the wiper arm lift up the plastic cover to gain access to this nut!
If you dont understand take it to a mechanic cost will be minimal. In fact that is what you should do!