Vindicator Xayann at the Shattered Sun Staging Area wants you to place the Attuned Crystal Cores inside 5 defeated Erratic Sentries to turn them into friendly units.
5x Converted Sentry Deployed
My plan to replace the damaged crystals on the erratic sentries has been a success. We've managed to take the Sun's Reach Sanctum with their help.
I've crafted new crystals that will bring more of them under our control; place them inside the hulls of defeated sentries. We'll deploy them to other locations once they're converted.