What you are looking for is a salt bath, which will kill off the fungus. I would also set up a seperate container that you can keep Molly in until the fungus has cleared up. This container doesnt need to be huge, enough room for her to move in comfortably and you need to do 100% daily water changes with water that has been dechlorinated and is the same temperature. Hopefully this will prevent your other one from getting it. Might be a good idea to get some Indian almonds leaves for the main tank.
You just need to be aware that fungus is a secondary issue of an underlying problem in the tank; something is stressing out your axolotls and causing the immune system to be suppressed enough that the fungus could take hold. Temperature is a HUGE culperate here, though your water parameters or even water flow can also cause stress. Until you solve that issue, you cant prevent this from happening again.
How to Salt Baths
Put dechlorinated water in the container (tapwater treated with water ager/conditioner/dechlorinator drops to remove chlorine and chloramines).
Add 2-3 teaspoons of salt per one litre (or two pints) of the dechlorinated water.
Give it a stir (or if the aquarium salts are chunky, crush them) until salt dissolves.
Remove your axie from the tank, place in the saltbath and cover with lid (so it doesn't jump out.
Leave your axie in the saltbath for 10-15 minutes maximum, no longer. Salt baths are very stressful for your axolotl and, with their permeable skin, more than 15 minutes can be harmful if not deadly.)
Saltbath your axie twice a day until at least a week after the fungus drops off.
Empty the saltbath water and clean the container using baking soda and water.