Remember to always backup your original saves, download only from reputable communities like Speedrun or Nexus Mods, and keep your master backup in the cloud.
Copy the downloaded SaveGame00.tot (or whatever slot number) into your active Total Overdose folder in Documents .
Ensure the file you download is a .tot (Total Overdose Save) format. If it comes in a .zip or .rar , extract it using WinRAR or 7-Zip.
Rename your current Total Overdose folder in Documents to Total Overdose_Backup . If something goes wrong, you can revert.