Most (all?) modders use Adobe Animate CC (or the former Flash Pro CS/CC) to make FLA files that are "published" as SWF files.
Basically, one cannot "convert" static PNG files into dynamic SWF ones, because PNG is raster graphics while SWF is vector. Also, PNG files are just a bunch of pixels, while SWF contains some code.
Automatic conversion of raster to vector is possible, but the result is too crappy to be used for SDT (example HERE).
If it exist, it is possible to convert the base SVG file used to make the PNG file into a SWF, but the result will still not be dynamic.
To make dynamic hair, one need to cut the strand(s) into several pieces, draw an half-disk on top of each and arrange them in a specific template of the FLA file.
If no SVG file is available, everything need to be redrawn from scratch.