OK, I have researched a bit and it may be possible to use Bulk Rename Utility: https://www.bulkrenameutility.co.uk/
The Bulk Rename Utility er a very powerfull and complex tool, so I strongly recommend you work on a copy of your data and then replace the original files once everything looks good, this has saved me from catastrophe a couple of times 
That is: COPY data data_new; WORK on data_new; VERIFY verify verify; RENAME data data_old; RENAME data_new data.
Here is a quick introduction to an approach that may be modified/extended to handle your situation:
First enable Renaming Option/Prevent Duplicates.
Then enter one or more character conversions:
Then select the files to be rename and click preview and verify the new names and finally click rename - et voila:
The proposed solution is heavily inspired by this:
https://superuser.com/questions/327816/convert-file-names-into-utf
Another solution if you are good at linux and knows the codepage you are converting from:
https://askubuntu.com/questions/568565/how-to-rename-file-names-to-different-encoding