If you have already posted a packing slip, but need to re-print it, there is a slightly different method to do so.
Find and select the Sales order who’s packing slip you wish to re-print.
Navigate to the “Pick and pack” tab.
In the Journals area, click “Packing slip journal”
This will open the Packing slip journal window.
Select the packing slip journal to print, and click the “Preview/Print” dropdown button
Click “Original preview”
This will open the Packing slip preview window.
From here, you can print as you normally would.
Click the “Close” button when finished.