Your Save Game files can be located within your ‘Documents’ Folder within the ‘Sports Interactive’ folder.
By default the save game location will be as follows:
Windows
C:\Users\[Your Windows Username]\Documents\Sports Interactive\Football Manager 2018\games
Mac
/Users/[Your Mac Username]/Documents/Sports Interactive/Football Manager 2018/games
Linux
/home/documents/Sports Interactive/FM2018/games