Book keeping. Its like the little sibling to an accountant that does all the boring/tedious data entry but you don't need to sign your name to any state/federal attestations that tax math has been done properly.

If you think you need a "course", you should be able to find something that can give you the basics by searching Free Book Keeping Course. If you've got an account with some of those job search websites like Indeed or LinkedIn, they might have "certification" courses for free/cheap.

Libgen.is will pull up a bunch of entries for books about doing Book Keeping that are between 200 and 600 pages.