though i would hestitate to recommend a treatment w/out a much clearer pic (that would be quite the irresponsible thing to do)-a drop of malachite green, applied directly to the 'fungus', if it is that, w/a q-tip, -should work
dip the end of a q-tip into some malachite green, and touch the patch directly with the tip-while the fish is gently held in a net
though a better pic would be advisable, first-for it could also be lymphocystis-something which many angels get
if it's lympho-it can be very gently scraped off the fish-even a partial removal usually seems to trigger an immunoresponse from the fish-which will then, usually, fight the rest off by itself
hth