Hit the marker just by the Shield Wall to continue the season finale.
You'll now have control of Seoul's Defenses. They work just like Gremlin Tech, but you have infinite number of shots (though the cooldown remains inescapable). Get a feel for the new weapon as you reach the first blockade on the way to your objective.
Fight your way to the functional elevator, using defense blasts and standard techniques as you like.
On the next level, it's Ice Barrage Cannons again. They're so weak you're almost better off scragging them with traditional fire, and saving the defense blasts for enemy mobs, particularly the 'fortified areas' that Friday points out to you.
Victory draws some Shocktrooper attention- kill or evade as you like, but follow your marker to a hackable console when ready.
Ride the platforms up and annihilate enemy forces here, culminating with the second and final story mission golem.
Another hack, another platform ride. Use your blasts to take out the shield generator defenses, though keep a special eye out for those pesky snipers.
You'll have to do more platform switches to reach the shield generators- for some reason the enemy always rides along with explosive barrels, so shoot those for a quick clear.
Take out the generators themselves to open a way forward.
When both are gone, hack the indicated console to eject Dr. Babylon, then use the Seoul Defenses to destroy the control room. The game doesn't make it specific, but aim your shot at the central TTX building to meet your objective.
This final act of massive destruction completes the mission.