Add this snippet to bl_UserMetaData.cs in RawData class:
public int Reticle = 0;
Go to Assets\MFPS\Content\Prefabs\Presents\Settings\ and you have to add values to Default Settings [High] and Default Settings [Mobile] depending on which MFPS you own. While either of them selected, add new elements in Setting Values list. This is how it should exactly look:
Run integration by going MFPS > Addons > CustomCrosshair > Integrate and follow the steps.
After integration is successful, you should see it in Options > HUD.