If you are looking to download or revert to this specific version, the process depends on where you own the game:
Here's a review of the update:
: To keep this version safe from future updates, copy the entire "Kerbal Space Program" folder from steamapps/common to a new location on your drive. Private Division / KSP Store Users Log in to your account on the official KSP Store . Navigate to My Account and find your KSP purchase. Click the Download icon and select your OS. Ksp 1.12 Download