You'll need an appropriate adapter to connect your monitor to your GPU.
For example, I have three monitors, they only have DVI and HDMI ports on them. My 980Ti has 1 DVI, 1 HDMI and 2 DP ports. One of my monitors I picked up a HDMI to DP adapter ( https://www.newegg.com/Product/Product.aspx?Item=N82E16812119557 ) so I can connect it to my GPU. My other two monitors; 1 connects to the DVI port and 1 connects to the HDMI port.
In your situation, you'll need a DVI to DP adapter to connect your second monitor to the GPU.
I assume your second monitor has a DVI input, but no displayport or HDMI inputs. You can still use one of the Displayport output ports on the GPU. You'll need a displayport cable and a displayport to dvi adapter.
You'll need an appropriate adapter to connect your monitor to your GPU.
For example, I have three monitors, they only have DVI and HDMI ports on them. My 980Ti has 1 DVI, 1 HDMI and 2 DP ports. One of my monitors I picked up a HDMI to DP adapter ( https://www.newegg.com/Product/Product.aspx?Item=N82E16812119557 ) so I can connect it to my GPU. My other two monitors; 1 connects to the DVI port and 1 connects to the HDMI port.
In your situation, you'll need a DVI to DP adapter to connect your second monitor to the GPU.