Kannamyacin and nitrifurazone are the chosen meds used together to defeat columnaris.
They are sold as seachem Kannaplex and Furan2.
A hospital tank is BB(bare bottom) heater, filter and water.
Quickie is water from main tank and go.
No cycled filter as meds will kill it so you have to change water daily or as needed in hospital tanks.
I always change water when using meds to make them more effective.
Almost every med says to do a large water change first as nutrients in water will weaken the meds.
These are the links to read on columnaris;
Fish Columnaris | Fungus & Saprolegnia | Treatment & Prevention