Interact with Part(page) record

Good morning everybody.
I’m working on a page that contains shipment headers, inside this page there is a part page inside, displaying also the shipment rows.
My goal is to implement an action button, that reads trough the records of the part page(shipment rows) and prints labels only for specific records, the ones with the BOOLEAN flag set to true.

I implemented already this function without using part page, but opening the shipment rows page in a different istance, using a lookup on the header page.
Now i want to try with the part page, but i have not clear how to actually interact and work with the part page records. Do you have any suggestion for me?