Hi lorgeron!
I can show you how to reopen a closed purchase order (PO).
Let's pull up the PO first. Go to the Vendors menu and select Vendor Center. Select the vendor's name, find and double-click the PO.
Once done, we simply need to click the Mark As Open button in the header section. Then, don't forget to click Save & Close. Refer to this screenshot:
I also added these articles for your reference on how to properly track the transactions in QuickBooks Desktop:
Keep on posting here if you need more help with this. Wishing you all the best!