Automatic renaming of many subfolder from YYYYMMDD into YYYY-MM-DD

Dear All,
I have imported photos putting them into many subfolders named YYYYMMDD (of folders named YYYY).
Now I would like to rename the subfolders automatically into YYYY-MM-DD (letting the folder name by YYYY).
Please how can I do it?

Thanks you very much!
best Regards
fabrizio

Replace: (\d{4})(\d{2})(\d{2})
With: \1-\2-\3
Use regular expressions