Caius

So I recently had to uninstall and reinstall the Minecraft Java version to fix my computer. I downloaded the installers for both 1.14.4 and 1.12.2. The one for 1.14.4 works, but 1.12.2 doesn't show up in my Minecraft launcher after repeated tries at putting it in. I'm lost on what to do, and I really want to play the Pixelmon mod for 1.12.2 as it's the latest and only release of it. I could really use help on what to do, so any suggestions would be greatly appreciated.