Done this twice as I've had two wiper motors blow up on me in the past few years.
The wipe arm position needs to be correct before you bolt the wiper on to the arms. So run motor until its in the park position, disconnect motor from arms and reattach with arms in correct place.
Deducing the correct position is the problem, I got very close by referencing pictures of the assembly together assuming it was taken off the car in park mode.
For example link below:
Hope this helps