owwwhh, the black rot, it could spread out rapidly, so....
cut the black parts off, then give it a physan dip, or two. If you have no physan, use peroxide or any germs killer, then add an anti-fungal spray, place it down in some airy, light and cool place.... let it rest till no more blacks appears, to keep it hydrated, gives some light water spray each morning. if the black still appears, pull it out of its pot, clean the roots, and do the above. After it is recovered, repot using new and clean materials. Hope your cattleya survived