You’ll recall that in Avengers: Endgame, after they failed to secure the Tesseract in 2012 New York, Tony Stark and Steve Rogers traveled back to S.H.I.E.L.D.’s headquarters in 1970 to retrieve that era’s version of the glowing cube and some extra Pym Particles. It’s there, specifically in the underground bunker area, that Tony runs into his father, Howard Stark, and it turns out this bunker is also where Arnim Zola has been carrying out some special work, as you’ll notice below.
Article source: https://www.cinemablend.com/news/2478145/avengers-endgame-hid-a-cool-captain-america-the-winter-soldier-easter-egg