So, we all now Cap is gonna die in A4, but I read a theory(idk if it's true) but it's about how Captain America(Steve Rogers) dies.

So they travel back in time and they end up retrieving Mjolnir, Thor's hammer, and at one point, Steve uses the hammer to hold back Thanos(usING THE FREAKIN HAMMER MY LIFE IS COMPLETE) and then dies, allowing everyone else to escape. The end.