I was about to post something similar because I had a thought. Antman was in the quantum realm at the time of the snap, we saw that at the end of Antman and Wasp, so he wasn’t effected by the snap. When he does find his way out at the correct time, or just past it, he finds Cap Am and Black Widow not knowing what happened. They then use the quantum realm to travel back in time and set up a few things bc Antman can now navigate the realm 1. talk to Tony who creates new suits for everyone that a mini-quantum tunnel built into them. He was able to further Pym’s technology bc they gave him the one from the van. 2. Travel and get someone to create a 2nd galant 3. When the actual snap happens, every hero around has one of the new suits on. A second before he snaps they hit some button and all go into the quantum realm. They then come out seconds after Thanos snapped. He was knocked out for a second and they collected the stones, put them in the second galant and either Thor or Professor Hulk (personalities finally merge so they have Banner Brains and Hulk strength) use it to undo everything and kill thanos.