You are probably missing a go to layout step.
I only see fields in the portal and am not sure which table is the portal's table. I've guessed storeroom for this example:
Set variable [$Qty ; StoreRoom::Qty to Issue]
Set variable [$ID ; StoreRoom::__pkItemID]---> I can't tell which field uniquely identifies each item.
Go to Layout [Issued]
Set Field [Issued::Qty ; $Qty]
Set Field [Issued::_fkItemID ; $ID]
Go To Layout [original layout]