Firstly what happened? Secondly, the best treatment is if possible move the aro to a separate tank, up the temperature a few degrees and add aquarium salt(just a few teaspoons) that'll help the healing process, and do water changes often, like daily. Keep tank lights off for a while and do everything to keep stress down, so no tank mates, no glass taping or constant checking up and don't feed for a day and after that small feedings. If you don't have access to a separate tank do all the above and clean the filter.
I would go up to 86f for a bit as not to many diseases can live at that temp. This will reduce secondary infection as well but add an airstone to ensure enough diluted oxygen