I’d use this resource to retrieve the player if in Zone, then fire a RemoteEvent to the client and change & modify lightning settings to the wanted fog for the client.
@jojo2467 has made you it already in a place file.
Step 1: Open his place file and search for “LocalScript”. Look for it in StarterPlayer → StarterCharacterScripts and then add it to your place in the same way.
Step 2: There should also be a part with the name “FogDetectionPart” directly in Workspace, in your game.
Have you checked the script? I personally haven’t seen the file as I’m not sure where I can download them on mobile, but maybe the script wants you to set your own fog or your own variables…?