Plants have their own sense of time that isn't measured by the hour hand on a clock, rather, day length (technically it's the length of the dark period) is what the plant pays attention too. When the day length signals the plant to grow, and other cultural conditions allow it to grow normally, your plant should from that point forward start producing healthy growth. It can't 'repair' the damaged growth, though that will eventually be shed and forgotten as the plant grows. What you're seeing is probably the result of an ongoing shedding process that may well have been instigated by conditions that affected the plant even before you acquired it.

Your very best coursed of action is to make a good plan that A) ensures good root health B) takes advantages the plants more robust periods and makes allowances for when the plant would be better off without extra human generated stress C) has you ensuring cultural conditions in the area of light, temperature, and nutrition that subject the plant to the lowest level of stress you can comfortably manage.

Fortunately, these things are much easier than they sound, but it's not realistic to expect to see the results of your efforts in a month or two. Choose a course, stick by it, be patient. If the course is a good one, your plant will cooperate. If it's not, it will let you know.

Al

Your fiddle leaf issues seem to be the same as mine and it is very difficult to be an accurate water tester when you stick your finger into the soil. I have had mine for 12 months and have tried various things including watering weekly, watering monthly, Charlies Carp, repotting. My latest is watering every 3 weeks and alternating with water then fertiliser (Charlies Carp). It has only lost 2 leaves in the past month or so which is the best it has done since I bought it 12 months ago. I agree with some of the comments though, maybe try not to panic (I have been there) and just leave it alone for a bit. In my experience, less is best when it comes to watering. Good luck.