“Use Ghost to access a SIVA data store.”
“Access the laboratory” is an objective in the mission Download Complete in Destiny: Rise of Iron
Walkthrough[edit]
Just inside Overwatch you will find more Cabal coming after you. You have more Psions, Legionaries and Phalanx
Fight your way into the back room in this section. Just over to the left to find the server you are looking for.
Go over to the server and interact with it. Ghost will scan it and tell you that the data store you are looking for is below the room you are in.