Saltbath treatment is:
2=3 teaspoons of uniodised table salt/sea salt or aquarium/tonic salt per litre of dechlorinated water.
Make sure to dissolve the salt. If using the aquarium/chunky salt, crush it so it dissolves easier.
Then add your axolotl to the bath - s/he may find it a little irritating at first. Cover with lid. Ensure it stays in minimum of 10 minutes, but no longer than 15minutes.
Saltbaths need to be done twice a day during the week (or 3 times per day if able).
If fridging the axolotl make sure to put the saltbath in the fridge so it's the same temperature as it's fridging container to avoid fluctuating temperatures which can be just as stressful to the axie.
Empty the saltbath after each use and make up a fresh one each time.
You could also try picking the fungus off with tweezers if you feel confident enough to do so without harming your axolotl, a steady hand is needed though.
Continue with the saltbaths for around 4-5 days after all the fungus has dissapeared.