The best thing you can do to rid yourself of fungus gnats, is to cut back on the amount you water. Fungus gnats love poorly draining saturated soil. So if you over water your houseplants, the fungus gnats will thrive. There are also some BT containing insecticides that can help control fungus gnats. If you use one of these, read the label carefully and follow it. Even though it is an organic pesticide, it is still a pesticide and the label must be followed. Check to make sure your pots are draining properly and consider re-potting them in fresh potting media if it is older.

https://www.extension.iastate.edu/news/watch-fungus-gnats-house-and-take-action-if-found