How to get to wiper arms?

Look for a plastic cover that's snapped over the pivot. Pop that cover up and look for a nut. Be sure the arm is positioned properly, then tighten that nut.

Sorry to keep you waiting.

What exactly are you trying to solve, and which model do you have? It's pretty common for that pivot nut to work loose, and just tightening it makes the arm grab onto the splined shaft better. The symptom is one arm works normally but the other one either doesn't move at all or it sticks in various positions. There's no abnormal noise associated with this problem.

Another, less-common problem is the arm on the bottom of the shaft breaks off. I never fixed one on a Toyota, but generally the arm is just pressed onto the splined shaft, then the shaft is peened over to retain the arm. The fix is to remove the shaft assembly, tap the arm back on, and tack-weld it to keep it on. The alternative is to replace the assembly.

You should not have to go under the dash to work on the wipers. On a lot of newer models the entire wiper transmission and motor are mounted inside a large plastic bucket that can run the entire length of the bottom of the windshield. This is done more commonly on vans when there isn't real good access to the back of the engine compartment. You'll typically hear the arm / lever flopping around. That bucket is removed and unplugged, then it can be disassembled on the work bench.

I'm afraid I'm not familiar with that model. My best suggestion is to get a copy of the manufacturer's service manual. A good place to look is on eBay. There are online services too but they often don't cover things like this.

Wish I had a better answer for you.