For the most part, on the units I've seen, the degrees of motion at the pivot point; base of the arm; is not adjustable. Only the arm length and the secondary angle control near the blade mount have any adjustment.
The arm may have come loose on the splines at the pivot, shifted over the curve of the windshield and stripped.
Look first at the lock screws on the blade end of the arm, check for loose screws and movement, paint pealed. If all seems ok there , remove the arm from the pivot and check for damaged splines on the arm, the pivot is steel , the arm is pot metal and will strip first, if the splines are gone, you'll have to find a new arm.
The next place where damage may occour is the bushings in the pivot it's self, check for wobble and up and down movement, then you have to go behind to the linkage from the motor to the pivot, the links there have end bushings that can wear out. But usually when they do they fall apart.
Hope it's only a loose screw.