The latest revision of Intrasis is 5950, published 2018-05-31.
If you already have an installation of Intrasis 3.1.1 you can upgrade to 3.1.2 by downloading Intrasis Patch.
Unzip the downloaded file on your computer and run the setup file for your version of ArcGIS e.g. Intrasis_Patch_126.96.36.19950_[ESRI_10.4].exe. Make sure to run as administrator. The patch will be installed, and it will only take a few minutes.
If your computer doesn’t have correct versions of e.g. Microsoft Visual C++ 2013 Redistributable, needed by Intrasis, they will also be installed. Some computers might need a restart after installation of external packages.