Now that you have your sequence created, you will have to add an Iterator Step.
Start by adding an Array into your Sequence (click on your sequence and look for the Array component in the palette), drag & drop it into your Sequence and then look for the Iterator in the Palette and drag & drop it into your Array.
Double click on your Call Transaction to open the Source Picker, where you have to find the "sql_output" to integrate it into the iterator but, indeed, we cannot find it..
This is because you need to update your transaction schema.
To do so, right click on your transaction named "get_references" and click the "Update schema from current connector data", then double click again on your Call Transaction : The SQL output is here !
Open this sql_output item and Drag & Drop the "row" field on your iterator.
The sequence will now loop through the Database data.