I do not want you to break this or ruin this but, for me, this would be a simple matter of removing the front ring (should screw off) and then unscrewing the metal ring that holds the element in place. Then I would use straight ammonia water and an ultra clean soft tissue and wipe it clean. Most likely the fungus (or most of it) would come off. I do this sort of thing every day.

With due respect, Mustafa, I have not found that to be the case with fungus spreading to other lenses. Fungus grows in dark, moist environments and if it is not too advanced, can be washed off. If left to grow thickly, it can etch into the glass. Still, in those cases many days in bright sunlight (by the window) can lessen this annoyance. - David Lyga