Yes the topical treatment is called fungicide. I disagree with Luke, the extra humidity is likely a positive but I would raise the 'tent' up a bit using something like chopsticks and provide a small 'vent' opening. Having it on a heat mat totally enclosed in that close fitting tent you are risking cooking that cutting.
Why did the person you got this from remove the only root that you had? I don't mean to be the storm crow bearing bad news but this cutting has an extremely poor chance of survival. If anything happens, rot starting at the root or either end, there is nowhere for it to go except to destroy the single node you have.
I would personally petition for a refund from whomever you purchased this from.
I am including a photocopy here of a table that was comprised by a few very experienced aroidists concerning the likely viability of Monstera cuttings. It was created specifically because so many chopped up snips of Monstera stems are being sold as 'cuttings' for astronomical sums of $$ that they got fatigued trying to answer the 100's of people posting photos just like yours. I am not trying to be harsh, but I can tell you from personal experience that your cutting has only a small chance of rooting and becoming a plant. I have been growing variegated and non-variegated Monstera for about 15 years.
Welcome to the site, we have a dedicated Aroid forum here, if you are interested in that Genera of plants we would welcome your participation.