Library Clean-Up

I have a library of classical music on a hard drive, about 1700 albums, 18,000 tracks that I am trying to manage with Roon. The problem is that Roon does not identify correctly some tags.

E.g. I have 102 “works” by composer “Johannes Brahms” that are correctly identified and 88 “works” by composer “Brahms” that is identified as a different composer. (In my library, all the file tags have “Brahms” as composer).

It is even worse with the artist tag. Not only I have 25 “Otto Klemperers” and 10 “Klemperers”, for many albums/tracks the artist is not identified at all.

How do I clean this up?