Set up a quarantine tank, if possible.
A heater, a HOB filter, a bottle of bacteria, an ammonia badge . . . and a box to hold water.
If a fish with ich was in your display for two days, then all the fish in your display (are there other fish in your display?) undoubtedly have it as well. If they don't, they soon will. You'll need to remove any fish from the display, and treat all in either TTM (Tank Transfer Method), copper, or CP (Chloroquine Phosphate) for 30 days - but hold them in QT until your display has been free of fish for a total of 76 days. - Or investigate "ich management" (not appropriate for all fish).
~Bruce