Thanks for this video. I often can't really tell if Warren is purposefully being disingenuous to score political points or if she is just confused. As detailed in comments here, there is no direct "subsidy" from the government to these banks. What exists is an implicit guarantee that very large banks will not be allowed to fail, and are therefore less risky to investors, allowing the banks to borrow money at a lower interest rate. Bloomberg went and attached a value to this guarantee, at $83 billion.
So, the way to remove this guarantee is to allow the big banks to fail. The person in charge of such things is the head of the Federal Reserve, in this case Ben Bernanke. Warren's first question after describing this policy, "Should the big banks be repaying the American taxpayer that 83 billion dollars?". This question is phrased in such a way that implies they should be repaid, but of course this is nearly impossible because this money was never paid to the banks directly in the first place, but he can't say no because then it looks like he is defending the big banks. So Bernanke tries to explain that this "subsidy" is based on expectations and market forces, and that the best way to end that is to improve the authority and ability of the government's Orderly Liquidation Authority, so that these banks can fail in a way that doesn't disrupt the entire system. But then Warren asks him again later, what happens to the $83 billion in the meantime, and if can be paid back.