The most important thing is to make certain the fish is in its one quarantine tank to prevent further infection of the other fish as it is a viral infection. Once in quarantine treat with the treatments mentioned earlier, along with making certain the fish has easy access to air and the lights are dimmed. The next step is to sit down and calm yourself while preparing to wait it out. It will take time for the virus to run its course and there is no guarantee that it will survive but since it isn't a juvi it has a much higher chance of survival. Don't be concerned with iratic swimming behavior as it is just a symptom of the virus.