Fredo6 has plublished many extensions. Which extensions do you need? Maybe you want to purchase the bundle which would save you a bunch of money. The extensions included in the bundle are listed here.
As I indicated, you should install the Sketchucation Tool first and use it to install the extensions you are after. Get it from the Resources section. Also look at the dependencies for Fredo6’s extensions. Most require LibFredo6 which you can also install via the Sketchucation tool.
Are you still using SketchUp 2019?