Navigate to your game directory (usually SteamLibrary\steamapps\common\Grand Theft Auto IV\GTAIV ). Delete everything inside the folder to ensure no modern files conflict with the old ones, or simply point your downgrader tool to this path. 2. Use an Automated Downgrader
The latest Rockstar Launcher version uses a stub GTAIV.exe that launches the real game from a separate directory. You need to bypass this. The downgrader tool will handle this, but you can manually do it: downgrade gta iv to 1070