HP Intel Dual-Core Slimline Desktop

I bought this to use with a dual-monitor set-up for working from home, but the plug-in for the monitor on the back of the p.c. does not match the cables that came with my (also HP REFURB, purchase from Woot at the same time) monitors. The set came with 1 converter, but I need another one. What is this converter called so I can buy it online?