Replace rear passenger window

My car was broken into (for a bunch of empty grocery totes...); the main rear passenger window (not the small one) was shattered.

Bought a new window, cleaned up the old one and cleaned the shattered glass out of the metal thing that hlds the window (and I guess attaches to the regulator), and got the new window attached to that metal piece. (I didn't do that...my friend who is a mechanic did.)

However, he can't figure out how to install the new window. Does the tiny window need to be removed first? Can anyone tell me how to install the passenger rear window in a 2017 Prius? This shouldn't be so hard...but it's not like any other window he has replaced. There's info for 2010-2015 models on the internet, but nothing for Gen 4 which is...ominous...to me.