To install:

1. go to: C:\Users\(your user)\AppData\Roaming\Sekiro    there is your savegame. extract everything in there to another location. if you don't do this, you are going to loose your own savegame.

2. Open the download and open the folder inside that says: savegame.

3. extract or drag and drop the two files into: C:\Users\(your user)\AppData\Roaming\Sekiro 

4. you are done and can now open the game with this savegame

ENJOY!