There are three possible DedSec contacts you have to talk to to get this mission started:
+9000
Head to the marked location and fly your quadcopter to find Victor Cheung. Hack his phone safely from the air using your quadcopter to complete this objective.
+9000
Drive to the meeting area only to find it empty. To continue your investigation, you have to find the phone inside the container van. Use your jumper to find the opening of the container van in the tight space at the back to hack the phone inside, in the middle of dead bodies. This will complete the objective.
+9000
Swelter Outfit Sun Cap
Drive to the marked location to help Aiden Pearce, the previous game’s vigilante protagonist. The area is restricted and you have to physically hack the ctOS junction. Send your jumper to infiltrate the bunker. There are only a handful of guards here you can easily circumvent or trap. After successfully reaching the ctOS junction box, hack it to get a camera view of the cell where Aiden is held. Wait for the guard nearby to walk into view then hack his phone to distract him. Aiden will take this opportunity and escape. After the connection has been severed, leave the area to complete the mission.