Help with Make Change to Thing list workflow

I have 2 things (databases) I’m using for this workflow. The diagram below illustrates the structure:

The left side illustrates the Watch History database. The type of content for this group is a “User” type I created. It has a text field for the user (uses a text email address). Note that the list outlined on the left side of the figure only shows the watched titles that belong to the user that’s logged in. It also has a field for a list of Watched Titles, which is an “Exports” type coming from another database.

The Exports Database contains a list of Movie titles (text). The content for this group is set to “Exports” type. This is where the Watched Titles in the Watch History Database is coming from.

On the right side of the figure, is a repeating group of movie titles from the Exports database. I would like to implement a feature that adds the title for the given row, to the current user’s list of existing “Watched Titles.” When someone clicks the “Add Title” button, the movie titles on the row will be added to the current user’s Watched Titles list (maybe a :plus) operation.

When I go to add an action for the button, I’ve tried “Data (thing)/Make Changes to Thing” but having a hard time getting the input parameters to take.