1. Run the script from the App Store menu (See Screenshot "Store Menu")
2. Select an object that has a Slice modifier on top of its modifier stack.
3. Run the script. The SNAP will be turned ON automatically.
4. Pick 3 points in the scene. After 3rd point is picked the Slice Gizmo will be aligned with the picked points. 

The installer that ran when you downloaded this app/plug-in from Autodesk App Store will start installing the app/plug-in. OR, simply double-click the downloaded installer to install the app/plugin.

You may need to restart the Autodesk product to activate the app/plug-in.

To uninstall this plug-in, exit the Autodesk product if you are currently running it, simply rerun the installer, and select the "Uninstall" button. OR, click Control Panel > Programs > Programs and Features (Windows 7/8.1/10/11) and uninstall as you would any other application from your system.