How to get rid of fungus ;_;

Some kind of fungus showed up in my begonia’s terrarium. I think it’s also showing up in my second one. So far I’ve sprayed it with a kinda natural, vinegar-based product, and I tried removing it with a spoon, but it’s hard to get all the white blobs + there’s definitely more in the soil, not visible. What can I do? Would a soil change help? I’m worried it’d just spread to the new soil :/