1. Locate the ENGINE_SETTINGS.XML file in the games files which can be found in Steam\steamapps\common\Alien Isolation\DATA

2.Open the ENGINE_SETTINGS.XML file in Notepad and find the following line of text <Setting name=Field Of View>

3. Directly under <Setting name=Field Of View> in the file, add the following text <Quality name=90 float=90.0 precedence=8/> You can change the number 90 to which ever FOV value you want.

4. After you have finished adding FOV options, you will need to save the file by either using File>Save or pressing CTRL+S.

Note: If you want to add more FOV options in the file, you will need to change the precedence number to one higher than the number before.