You can pass a law that essentially pardons existing convicts as well as changing the law for future cases, though not saying it's called for in this case. Here in AZ, some guy got convicted in one of our marxist counties for killing someone in self defense. The legislature clarified the law, and specifically made the new rules retroactive to fix this guy's situation. I think they may even have mentioned him by name. (Actually they did so twice, and once Manet NapoliReno, noted Marxist, was no longer the Governator of AZ, it was signed into law.)
Not sure how Congress can change Texas law, however.