Add this to your StarfieldCustom.ini
------
[Camera]
fFPWorldFOV=X
fTPWorldFOV=X
------
X= desired FOV in deg
Close down the game before trying to edit the ini file
My documents/My games/Starfield
Copy Starfieldpref to desktop
Edit Starfieldpref to StarfieldCustom
Open StarfieldCustom, delete all lines in it and add the ( replace X with the FOV value you want)
[Camera]
fFPWorldFOV=X
fTPWorldFOV=X
Save StarfieldCustom file
Now put StarfieldCustom back into the Starfield Folder
Run the game