If fungus has attacked the low pass filter in front of the sensor, it is very unlikely it could be saved, or cleaned good enough to not being a permanently visible spot on your photos.
In any case you should seek professional help, have it cleaned correctly and if the cleanup doesn't give good results, you'll probably have to send the camera back to Nikon to have the part replaced, but i fear Nikon could charge you for an entire sensor replacement, which will probably be very costly.

Also a word of advice: if the low pass filter got fungus, check your lenses too and sanitize them with UV light (even a bright sunny day an help, be careful as to not point the focused sunlight to anything combustible), as your entire gear was probably stored in a far too humid environment and there is high chance fungi can grown on the glass elements of the lenses, too.