Does anyone know how to add a film to the database?

I wanted to add a few short film collections to a collection since I own them physically, but even though TMDB has them, they won’t show up on Letterboxd since the ID apparently doesn’t exist.

For example: one that I want to add is “Tom and Jerry’s Greatest Chases” which is listed on TMDB as 266678 in the URL. I paste it to Letterboxd, and it says that it’s invalid.

Anyone know a workaround?