Talk to Sitara in the Hackerspace to trigger a scene and to start the mission.
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After the scene, make your preparations then head out to the New Dawn protest. Once there, start the mission. Find the vent where your jumper can enter in the northwestern part of the church building. From there, you should prioritize getting the access key first from the laptop on the desk in the first floor. Use the NetHack view to see where the access key is located.
After getting the access key, you can now infiltrate the building from the balcony by the street. The profile data stored in the laptop requires physical hack and Marcus near its location so use the scissor lift nearby to reach and climb over the balcony. Get rid of the guards as you see fit; either through lethal means or stunning them. If they spot you, some of them will be actively calling for reinforcements so you'll have to defend your position until the download is complete. Once done, immediately leave the building from the balcony again, find a vehicle, then speed off the mission area to complete the objective.