Avengers: Infinity War - 9 Ways It Sets Up Ant-Man And The Wasp, Captain Marvel & Avengers 4
2. Time Travel, Alt-Dimension, Or Something Else?

The easiest way to undo Thanos' actions would be with the Time Stone, but since that's now on the Gauntlet and in possession of the Mad Titan it's not going to be used for that anytime soon, unless he has a major change of heart. So how else could they reverse it?
Time travel could still be an option, and it's not *completely* out of the realms of possibility for someone like Shuri or Tony Stark to invent a way of going back, although it is a stretch. But could it be a mix of time travel and alternate dimensions?
With Ant-Man and the Wasp able to hop into the Quantum Realm, a place where time is meaningless, might there be a way of using that to then go back in time? Or might it be a more 'straightforward' case of using the multiverse that the QR opens up?
Another alternative is Stark's B.A.R.F. technology, which was designed to help the user forget traumatic memories, but could instead be used here to discover some crucial details from the past that will change the future.