Are you talking about the child table filter?
Then apply it
frappe.ui.form.on('Test DocType', {
refresh: function(frm) {
if (frappe.session.user == "user1@testmail.com") {
frm.set_query("item", "test_child_table_1", function () {
return {
"filters": {
"item_group": "Products"
},
};
});
}
}
});