Do you mean the topical Fluoride
that the hygienist applies at the dentist? The taste of that should go away on its own in a couple hours.
If you mean toothpaste, I have never noticed that Fluoride has a "taste." toothpaste itself has a taste that you can rinse away with water after brushing. If your toothpaste tastes bad to you and leaves an aftertaste, try switching brands.