The specific path for the savefile can be found in:
C:\Program Files (x86)\Steam\userdata<steamid64>\989690\remote\save_game;
Where is your unique steam ID, for example
Additionally, there may exist a temporary version of the save file here:
If you are copying an older savefile over from another PC, you should put it in the first location indicated above, and also remove any old save file from the Temp folder. This ensures the correct savefile is loaded next time the game is started.