Fetch from child table to child table

I’m trying to fetch a field only temporarily while I import the rest of my opening invoices. What I’m trying to do is fetch item_name from Purchase Invoice Item child table TO item_name on Payment Entry References child table.

frappe.ui.form.on(“Purchase Invoice Item”, “item_name”, function(frm, cdt, cdn) {
var d = locals[cdt][cdn];

	frappe.db.get_value(**THIS IS WHERE I'M LOST**;


Any assistance? THANKS!!

I gave up and am just going to hand write the invoice numbers on here. Opening Invoice Tool should have a field for supplier invoice and that should be standard. Not sure why it has “Item Name” instead but then you can’t actually use that in other places. Seems kinda wonky.