In Avengers: Endgame, Thor brings back Mjolnir (his hammer) from the past to his “future” self through the quantum tunnel. Later in the movie, Captain America gets hold of it being worthy.
However, I don’t remember if Cap takes it back to the past in the climax. If he doesn’t – that would break the spacetime continuum, Mjolnir being destroyed in the past.
If he does bring it back, how come he knows the exact time and place to return?