How do I create a Master Movie ID?

[J___T]

Master Movie IDs are missing for nine of the first 36 DVDs I added to "my collection." All of these have a page here, most have a photo, but there's no cast list. Therefore I can't add a cast list to the product page. (Several DVDs I sought to add don't even have a page).

So I need to learn how to create Master Movie IDs.

Thanks to anyone who can direct me to an official explanatory tutorial, or who can explain it to me here.