Help: Need to turn off "Enable Fog" but not found.

Hello everyone this is my first post.

I started playing "Fushigi no Dungeon Furai no Shiren"
using the latest Project64.

the problem is that the underground dungeon
floors are all emulated as plain black.

I found a Japanese compatibility site and they were advising
to turn off "Enable Fog" option but there seems to be no setttings
for this anywhere.

Could someone help me fixing this?

Thanks a millions in advance