You can find these older installers in the KiCad Windows Repository . How to Install KiCad on Windows 7
Right-click the installer and select "Run as Administrator" to ensure it has the permissions to register system DLLs.
Even as an older version, it includes the 3D viewer, Push-and-Shove router, and extensive component libraries.
Version 5.1.x was built specifically with Windows 7, 8.1, and 10 in mind.
Ensure your Windows 7 is updated to Service Pack 1 (SP1) . Without it, many of the C++ redistributables KiCad needs will fail to install.
Most Windows 7 machines are 64-bit; look for the x86_64 installer (approx. 1.2 GB).