How to access Mass Effect 2 DLC?
Solution 1:
To install your DLCs, you have to go onto the bioware page and download the installers. Log in and download them here. Steam doesn't handle any ME2 DLC and this is one of the reasons why there have been issues between EA games and Steam.
Solution 2:
Download all the DLC installers from here:
https://help.ea.com/en-ca/help/origin/origin/download-dlc-for-classic-origin-games/#masseffect
You have to run each one (they are installer exe files).
If you have issues activating them see this question: "Communication with the Mass Effect 2 server was interrupted or has timed out" error?