Hi GS5,

I added a sketch, showing how I go about it.

I make a goo out of scrap pieces of ABS, solved in Acetone or MEK, both will work, make it thick, not too runny.

I glue a strip of ABS onto the edge I want to sharpen, using a small amount of goo, or just a drop of solvent.
Once set, I fill the gap with the goo, higher than required, as it will shrinkg once the solvent eveporates.
Work in thin layers, as the solvent will also soften the surrounding ABS, too much solvent wil cause deformation (and more repairs).

To avoid the goo from running to the sides, I close those gaps with tape, preferably polyester tape, as it is less affected by the solvent.

Once the solvent has eveporated, over night, you can file, sand the edge sharp.

Regards, Jan.