I'm running a Magento site and we got an order of a multiple products, after a few days 2 out of 5 products were returned.
How can I remove the products from the original order and back to the inventory?
If you are using Enterprise edition, there is RMA functionality that could be quite useful for this return and others. I highly recommend it.
Also, if you want to automatically return items to stock when you issue a Credit Memo that setting is in the Configuration tab - here's details on how to do that.
Let me know if I can help with any other questions. Good luck!