When you receive less than the quantity on the PO for any item,  the status of the PO will become “Partial”.

When you click on the PO (Edit icon),  you will be able to see the number of units that have been received.

Click on the green Receive button to receive any remaining quantities.

If no more quantities will be received, you can close the PO by clicking on the three vertical dots at the top and selecting Mark as Completed.