How in the World???

There is a little stainless steel tab that acts like a retainer spring just lipping under the splined head of the wiper shaft. It’s part of the wiper arm thats over the wiper shaft head splines. It is facing the windshield under the arm. You may want to pry that out a little with a small screwdriver. Cover your screwdriver with duck tape to prevent scratches where it is going to contact your cowl or put some cardboard on the cowl.

Then after that put your screwdriver under the back lip of the wiper arm opposite the arm itself. Push down on the arm near the splined pivot head part while prying up on the rear edge. Push down and release the front hinge area of the arm gently while gently prying up on the rear edge. This will rock the splined portion of the wiper arm off the splined shaft. The wiper arm is like pot metal so make small wiggles and prys so as not to **** the arm too much and damage the splines.