That seemingly implied at the time the Avengers were the ones tracking down Thanos in order to restore balance to the universe and eventually found him, but now we know how they get started. The clip ends with a shot of plenty of Avengers in a space ship: Captain Marvel, Bruce Banner, Captain America, Black Widow, Thor, Nebula, Rhodey and Rocket. That’s footage, too, that was confirmed in a recent trailer.
Article source: https://www.cinemablend.com/news/2469405/we-saw-new-avengers-endgame-footage-and-it-revealed-the-heroes-plan-to-take-on-thanos