Have this part to work on. I .120 steel, customer supplied STEP file. The problem lies in the surface that joins the two parallel faces. Cannot convert to sheetmetal because I think the designer used an "electric hand-held carving knife" to shape the edge of this face. Not only is there not a flat face anywhere along this material thickness edge, but the boundary of the non-horizontal face is irregular. I believe it may have originated as a spline. I included a closeup of the area.

Anyway, what would be the best practive to fix the irregular edge/face so it can be converted to sheetmetal?

I really need to "resculpt" the boundary and edge of that flange.

Initially I started using delete face and patch but that function will not remove the .020 edge radius in the area of this "twisted/carved" edge (which also has the .020 radius). I have no idea how the designer generated this part.

I don't know if I have accurately described the problem with this model.