At the first vial of Toxin-A that the Soldier encounters
Okay, stop where you are. There's a vial of an experimental material called Toxin-A. It was developed by the Sci staff to reduce the growth of the aliens. But I can't find any data on how you should use it. You should be able to research the toxin. I'm uploading you enough cyber modules to acquire the Research skill if you don't have it.