Make sure to clean everything you are going to use in the new set up. Not sure if driftwood, sand/gravel, etc. is good to use anymore. Best to start from the beginning, keep and clean the tank, filters, heaters, covers, etc. only. Use bleach, as mentioned. Make sure to clean thoroughly as it can still come back. After cleaning with bleach, pour in de-chlorinator with water and let it sit for a day. Next day, dump everything out, rinse and let it sun dry for a few days. Hopefully it is still sunny/hot there. Just try not to set it up immediately as I did that and the columnaris came back even though I dumped the whole tank in a big tub of bleach and water mix.
Best to separate the sick looking fishes from the healthy looking ones. In my opinion and experience, once you are able to see the columnaris on the fish, it has no chance. I don't remember what medication I used but I overdose the qt tank with it and after 3 weeks, the healthy looking fish stayed healthy. The ones that showed it all died. That's how I lost most of my female bettas in my community tank.
