Hello, my name is XXXXX XXXXX welcome to JA.
There are 2 possible causes for this. Either the wiper motor mounting bracket is damaged or the park mechanism has failed. Many times, the small tab on the bracket that the park mechanism is designed to catch when the motor reverses to park, will get bent enough so that the park mechanism cannot catch it anymore..
This picture shows both the tab on the bracket and the park mechanism that should engage it. If you need to bend the tab on the bracket back into place, it is best to re-enforce it. I always put a little bit of a weld on them to hold them, but I think a really good epoxy would work also, as long as it doesn't interfere with the park mechanism.
The wiper motor is under the air inlet grille. You will need to remove the wiper arms and then remove the air inlet grille to access the motor. Procedure calls for a puller to remove the wiper arms, but if you remove the nut, they will come loose when you rock them up and down by grabbing the arm at the end.
Hope this solves the problem. if anything isn't clear, be sure to ask.