Open the plugins window in HDT (Options -> Plugins) and drag and drop the file you saved onto the window.
Enable the plugin and Restart HDT
Login then Connect your twitch account with this site
Streaming now functionality doesn't work (but don't worry streamer decks does)
You can check that it is installed by going to Options -> Plugins and also verify that it is enabled and which version it is
If it's not installing then perhaps HDT is installed in a non default location? Also check HDT instructions for installing plugins
For feedback or additional help see the #hdt-extension channel in my Discord
Include the hdt log file located here %appdata%\HearthstoneDeckTracker\Logs\hdt_logs.txt - this file is recreated if you restart hdt, there will be others in the folder so if it's in an old file