you can always save the plant, but not the leaves. first STOP watering... plants breath through their leaves.. (just like when you can see the moisture in your breath outside on a cold day). when they drop their leaves, they stop loosing moisture, so water less, not more. AND DO NOT do anything else different, don't fertilize, don't repot, don't move it (If it's already in a spot with sufficient light). they HATE change.
fiddle leaf are hugely temperamental, and when they tantrum, it's all the way, lol. I've moved one 18" closer to a window and it freaked out (maybe due to being closer to radiator, but not a lot?). they are really total brats.
Like a dummy (because I KNOW better) I bought a beauty this winter on a very cold day. it went from the big box store to the car, where I immediately took off my nice warm coat and zipped the plant inside, cranked the heat and brought it the house 10 min later. Over the next 5 days every single leaf dropped off.
I left it in the livingroom spot I chose for it, where it gets direct S sun (Feb in NY) planning to return it (they're not cheap).
Never got around to bringing it back for a refund, This is about 3 weeks from purchase, 2 weeks after the last leaf dropped, but if you look closely, you can see it's already got new buds. the top of the stem/trunk is history, dry and brittle, I'll cut it back eventually.
I guess, in short my advice is throw it out (just kidding,... kind of). your other option is to be patient, find a good spot where you get good light, will never ever move it , and underwater for the next 4-6 months, until you have actual leaves