Very unlikely. The dosing recommendations for Flourish are quite conservative. Most people end dosing much more as part of their regular fert regime. I wouldn't bother with a water change.
No, no worries, flourish is a very dilute fertilizer.
Had a spillage of Iron fertiliser (Fe plantain from Tetra) and now Fe test is 1.5 mgl. Is this too much and harmful? There is nowhere where I could find that says it is bad except you get BBA. Will the Fe eventually be consumed?
There's not a lot of info about the precise chemical composition of Tetra PlantaMin. It's supposed to be mainly iron (what form, it doesn't say), and it's supposed to have a combination of trace elements.
1.2 ppm iron is fine. In excess, but iron is of especially low toxicity. What concerns me is the other trace elements (but I'm not particularly worried). If you feel like, do 2 50% water changes. That'll cut your iron ppm to 0.3 ppm, which is a very safe, conservative level of iron (and it should sufficient dilute the other chemicals).