Before 2/22/20 After 5/15/20

Attached above is a before & after of my one of my Fiddle Leaf Fig trees. The before picture was taken 2/22/20 & the after picture was taken 5/15/20. I brought my tree home from my office on 2/21/20 & it suddenly lost all of its leaves these first two weeks of May. That’s the main symptom – the loss of all the leaves. I know now that the plant was absolutely not getting enough light, being located in a corner of my room quite far from my windows (which are south facing and already don’t get much light). The tree came to me overwatered, so I started out watering it once every two weeks for the first month and then weekly – giving it around 20-24oz each watering. There are 4 drainage points at the bottom “corners” (it’s a circular bottom so I don’t know that corner is the proper word for it) of the container and I have it seated on a tray. I’m not quite sure what soil it is, as it’s simply the one it came in – I’m a total newbie to plants, as you can probably tell. I’ve never added fertilizer of any sort although I did notice some green circular plant food that are in both Fiddle Lear Fig tree containers that must have been put in by their old caretaker.

Is there any way to salvage this sweet tree? Should I chop some branches off? Feed it? What do I do!! Help!!