My understanding is that while reducing the nitrites does/could slow down your cycling process, you have fish in there so you need to balance the cycling process with the health of the fish. I wouldn't water change the nitrites all the way to zero but 2ppm is quite high.
Flukes are treated with praziquantel, so meds like prazicleanse, prazipro. Other meds have praziquantel in a smaller dose mixed with another med, like paracleanse, API general cure. https://aquariumscience.org/index.php/10-6-flukes/