According to the support page
https://support.hp.com/us-en/document/c03364712
that PC has 3 internal 3.5-inch bays, so it should be easy to add another drive.
Here is the support manual
http://h10032.www1.hp.com/ctg/Manual/c04205252
It indicates there are 4 SATA ports and the second hard drive should use the SATA 1 port, which is typical, with the primary hard drive on SATA 0