After this step, you will be locked into the boss fight.
On the next round, you will be able to interact with a screen in the Planning Offices. You will be able to move a cursor over satellites, which reveals information about them. Find the one that does not show a Soviet or American flag, but instead a question mark. Select this one, and a laser will fire from space, hitting the satellite.
Infinite zombies will soon spawn, so you must head to the anomaly, and a cutscene will begin to play.