To download YouTube playlists in a single click on your Windows 7 PC or any other other PC you need to download a video download tool which is free.
To download the YouTube playlist download the 4K Video Downloader Tool at the below link.
Then after downloading and installing that video download tool go on to the next steps.
Then start a video on the playlist on YouTube and then copy the link from the browser and paste it into the tool.
Then press on the option or click on the option Download Playlist to download the entire playlist of videos from YouTube.