You can grab special-k in their discord server #nightly-builds.
https://discord.com/invite/specialk
After you downloaded the archive extract it and you will find a SpecialK64.dll file
Rename it to dxgi.dll and place it in your saints row folder. sr5 specifically, in the directory that contains "SaintsRow.exe"
Then just unpack the mod in the sr5 directory so that you have SK_Root folder in the same directory as the exe file.
Then you should be able to just launch the game and it should automatically do its thing