Move or extract the downloaded plugin file to the TouchDesigner plugins directory.
The default paths for macOS and Windows are currently the following (you may need to create the Plugins folder yourself):
C:\Users\<your username>\Documents\Derivative\Plugins\/Users/<your username>/Library/Application Support/Derivative/TouchDesigner099/PluginsOn Windows, you'll also need to right-click on the downloaded file, go to Properties and enable the Unblock checkbox at the bottom of the window, then hit Apply.