This is the repository for plop. Download the gui_plop_setup_3_0_7.exe from the release and execute it. Current version is 3.0.7.
https://github.com/davidlewistoronto/plop/releases/download/3.0.7/gui_plop_setup_3_0_7.exe
If you just want to learn more about plop, download the manual in the link
https://github.com/davidlewistoronto/plop/blob/main/GuiPlop%20Users%20Manual.pdf
For a helpful introduction see Martin Lewis' page