Minecraft wiki entry for Legacy_village_mechanics, associated text: After you've used the splash potion of weakness and the golden apple, the zombie makes a loud sizzling sound, emits orange swirly particles, and begins to shake violently. It takes a couple of minutes for them to convert, so go ahead and trap it somewhere, and make sure it doesn't burn in the sunlight, or hurt any nearby villagers. After a few minutes, the zombie villager turns into a regular villager, at which point you can let it out to roam the village or do whatever.