Thank you in anticipation for any assitance!

3 weeks ago, my husband volunteered to accept a cat palm from his office that has been unattended more than 4 months probably.
We discovered that around 50% of the root and soil had fungus in it. We changed the soil of the plant thinking that we may get rid of the fungus from the soil. We have done this 2 weeks ago.
We notice last night that the fungus apperead again on the surface of the soil.
How to get rid of the fungus from the root and the soil?
Any help will be huge as we would like to try everything in our capacity to save this plant if we could.