Adobe SWF tool (Adobe Professional?) is hard to get and it works in Windows only (? at least no Linux version)
However you can use FFDec to export vector drawings (defineShape objects) from SWF file to SVG (Scalable Vector Graphic) files, modify these files and replace drawings in SWF by importing SVG back.
There are some difficulties because many graphic editors converts vector graphic to raster (bitmap) image which renders drawing almost useless for Flash. Some other editors use some SVG features not supported by Flash, so no way.
However, I found an editor that works just fine with Flash SVGs: Inkscape
Inkscape is professional vector graphics software which runs on Linux, macOS and Windows desktop computers.
It's free and available for all operating systems.
Thanks to this editor, I just created undressed sprites for 6 characters that I couldn't until now because cloth drawing was part of body drawing. Also in 1/2 cases nipples are missing (copied from another sprite) and always slit is missing (had to draw).
Example is Library cafe waitress sprite (referred as Armacool in some now deleted wiki if I remember)
So now everyone can draw missing body parts.
I have to watch Inkscape tutorial series on Youtube first to use it the right way. But I haven't drawn in last 30 years and I was not good at as a kid, so I'm gonna pretty suck.