First, locate your FiveM Application Data directory.
The location of your FiveM install depends on how you installed it in the first place.
- Did you run FiveM.exe in an empty folder? If so that's where FiveM is installed.
- Otherwise, FiveM installs in %localappdata%:
- Press WinKey+R on your keyboard
- Type %localappdata%/FiveM in the dialog that opens
- Hit enter
(More about installing FiveM here)
Then, open the CitizenFX.ini file with a text editor like Notepad.
Edit the path on the IVPATH= line pointing to your GTA V installation if necessary.