How do I turn off the AWD on my 2016 Toyota Highlander Hybrid Platinum Limited?

Tires are fine. Front and rear have be realigned. No warning lights. Toyota dealer and independent mechanic have both looked at it. The rear end has been noticeably "loose" on any slick pavement for most of the time I have owned it. I would swear the the rear motor is out of synch with the front engine/motor. Last week I fishtailed on a two-lane highway, on icy pavement, while driving below the speed limit without turning, changing lanes, or braking. I have never gone into a fishtail in a front wheel drive vehicle.