See the attached pictures. I'm short on ideas how to cover or replace this piece. I can't afford a full tub replacement right now so that is out of the question. Thanks
Looks like someone slapped wood on it (with tape???) and the inevitable happened.
What I would do is pry the wood off and install a piece of PVC trim or planking (gluing would be the best option here but be sure to get one that supports vinyl), then use a siliconized latex caulk to seal it up.
Your wet wall should have extended a few inches past the face of your tub. My recommendation is to do just that.