The marketing for Avengers: Endgame continues to be vague in the best possible way. Without any huge spoilers (aside from Tony Stark returning to Earth), the trailers have done a very good job of giving us bits of new footage that don't tell us anything. It seems like Marvel Studios have taken a page of the new Star Wars movies when it comes to trailers since both The Force Awakens and The Last Jedi had great trailers that didn't spoil anything.
However, fans who saw the trailer on Instagram have noticed a tiny new detail in regards to the returning Ant-Man; he's holding a stroller bag. Now, this might sound anti-climatic but if you saw Ant-Man and The Wasp, you'll remember that Hank Pym's laboratory is in this stroller bag. Seems like they'll be using some of Pym's technology to get to the Quantum Realm, which makes a ton of sense.
At the end of Ant-Man and The Wasp, Scott Lang, Hope Van Dyne, Hank Pym, and Janet Van Dyne were helping out their ally Ghost by obtaining crucial ingredients from the Quantum Realm. Lang was warned about dimensions that can cause time travel in the Quantum Realm by Janet, before the family was reduced to dust by Thanos, leaving Lang alone and stuck. Expect that element to be explored in Endgame.
Fans will be able to catch Avengers: Endgame on April 26.