Help batch reformat file name date format from DD/MM/YY to YYYY-MM-DD

Is the DD/MM/YY at the beginning (or end) of the file names (not including the extension)? If so, I believe you could do the conversion with A Better Finder Rename. I think it could be done in ABFR with 5 or 6 text/character manipulation steps:

DD/MM/YY beginning structure

20DD/MM/YY add '20' prefix (assuming all are year 2000 or later)

20YYDD/MM/ move YY to position

20YYMMDD// move MM to position

20YY-MMDD// add hyphen at position 5

20YY-MM-DD// add hyphen at position 8

20YY-MM-DD remove //

Have a look over there or may have already read this method ?

Rename files, folders, and disks on Mac

Check out this app:

https://manytricks.com/namemangler/

On further thought, this could be done in ABFR if the DD/MM/YY is at the beginning or end of the filename; or at any fixed position in the filename. Unsure if it could be done in ABFR if the DD/MM/YY position is variable in the filenames. And my references (above) to moving YY or MM are to move the characters at those positions, not an actual YY or MM.