On each title page, there's an "Edit this page" on the upper right hand corner. Clicking on this gives you a drop down menu, choose "genres" (not "tags"!) -- fill out what you need to.
As far as I know, both genres and tags are canonized, so only fill it out with tag names that already exist in the database.
Remember to give the team a credible source (for example an official synopsis), just a "I watched it" usually doesn't cut it. The easier accessible and the more credible the source is, the higher the chance that it'll get accepted.
