I figured mine out quickly on my 2905SS after someone else explained it. If you take off the back cushion and stick your fingers down in one of the back corners, you should be able to feel a little post on the sofa frame, then on the seat frame you should be able to feel a little hook. Just lift up on the front of the seat cushion frame while sliding it back a little and then drop the front. It should now be hooked in, but if it doesn't hook, try to lift the cushion frame a little higher while pushing back and it will hook. Can't believe how easy it was once I was told where the hooks are located.
2016 Ultra Lite 2905SS
2014 Chevy Silverado 2500HD