Hello there, @Oreo13.

Currently, the option to edit packing slip isn't available in QuickBooks.

I can see how useful it is to have the ability to edit the ship date of the packing slip. As mentioned by my colleague KhimG, what we can do right now is to create a packing slip out of your customer's invoices.

But I want to let you know that your voice matters and I'm taking note of your feedback and suggestion to improve the experience we're providing.

For now, you can visit our Blog to learn what new updates are being released, as well as additional references while working with QuickBooks.   

Please don't hesitate to get back to me if you have any additional questions about QuickBooks. Have a great day.