The seal against the moisture needs to be done from the exterior. You need to get to that interface between the glazing bead and the glass and clean/remove all the old sealant, tape off for clean lines, and install a new glazing sealant.

My experience with repairs is on old windows, so take this advice with a grain of salt. If your objective is to remove the black sealant, I would start by trying to cut it out, to slice it out in pieces as best you can. I would start with an X-Acto knife type of tool and a razor scraper to remove it from the glass. If you believe you know what product was used, contact the company or do some internet research on what solvent removes it. You might experiment with trying acetone (get a bottle of acetone based fingernail polish remover).

You may not need to remove all of the black stuff. You just need to remove enough to apply something over it for a smooth look.

If you think you know what was used, why don’t you google the instructions/specifications for the product?

@windows on Washington: excellent good to know glazing sealant is what I'm looking for! there's actually no moisture issues thus far, it's been pouring rain the past 3 days with no issues, it's really just an aesthetic issue... all sorts of bugs have gotten stuck in the black stuff so I can imagine all the sanding dust when I sand down the trim to paint will stick to it as well. it's also dripping down from where it was placed at the top of the windows and looks very messy.

@graywings123 @Jim Mat thank you for the advice. the 3M is my best guess based on what it looks like from googling. I thought it would maybe look familiar to someone who could identify it haha. But good ideas and glad to know it's probably safe to remove with a knife, and I have Acetone and goo-gone at home :)