How to Dynamically add item to List?

I have an app that shows movies, I want to click a link in front of the movie image(plus sign) that will display a dropdown containing the lists the user has created.

The user will then select which list he/she wants the movie added to. All without changing views. After adding some movies the user would be able to go to the movie lists view and select any list to check the movies added.

I can already create the empty lists, but I have no Idea of where to begin adding the movies. Probably an action would do the Job, but I need some direction.
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