Install the latest version of Paint.NET. Make sure you use the classic installer. Installing Paint.NET from the Microsoft Store will not work for CodeLab development.
Install the latest version of Visual Studio (C# options). The free Community Edition works fine.
While developing CodeLab, it is recommended to use the FastDebug configuration. This skips the ILMerge operation, and allows CodeLab to run outside of Paint.NET.
Click the menu: Build > Rebuild Solution
If the build fails, you'll need to debug that first.
If the build succeeds, a window will open and you'll see
CodeLab.dllandInstall_CodeLab.bat