my understanding
Here we need a rehalogenating bleach - take the silver and re- convert it back to silver bromide. Then the next step is fixer, or if really adventurous - redevelop for a colour and b&w picture on the same paper - or develop in colur agian for more contrast, etc.
C-22 bleach might do the trick - 80g K ferricyanide, and 20g K bromide per litre. It does c-41 film in about 2.5 minutes at 38C; I use this for c-41. Treat it as toxic waste and take to the hhw depot when finished with it. It can be re-used. I keep my 'out of spec' c-41 bleach, and after filtering it a bit, use it on b&w prints that are slated for a redeveloping toner, like catechol etc.