You can find online documentaries via the library's catalog, GIL-Find, the same way you search for books and e-books.
The screenshot below shows some terms that may be useful to find documentaries: documentary films, nonfiction television programs, and documentary television programs. (In this example I've used the Advanced Search to enter all three, to cast the widest net.)
Then add some terms to narrow down the search to your topic -- for example: racism, discrimination, injustice.
Click SEARCH. Depending on what you entered, you may also get some books and other materials. To make sure you're looking at online documentaries, there's one more step:
On the left side of the results page, check off "Availability: Full Access Online" and "Format: Visual." This limits the results only to online items, and only to videos. Click APPLY FILTERS to narrow down the results.