How to add a missing movie on BetaSeries?

You can use this form to suggest a movie that isn't already on BetaSeries: https://www.betaseries.com/films/ajouter

Once you're logged in, it is accessible from the Community > Suggest a movie menu, as well as from the Contact support page.

It will then be added automatically to BetaSeries.

If you can't find the movie through this form, you can sign up and add the movie on TheMovieDB, which is a collaborative site, then suggest it again on BetaSeries.