Hello!
There are several programs on the Internet that serve what you need, I leave one here but there are many more, it is a thing to look for, also to tutorials on youtube
http://www.nchsoftware.com/surveillance/en/index.html
Now, I suppose you already did tests if the dvr has problems, the only thing that is missing is to connect it to the pc on a network card, you must create a domestic lan so that the pc can recognize it to the dvr. The settings in windows can be found in creating a local network (you must use an Ethernet network cable)
The other option is with a video cable, as this tutorial explains.
https://techlandia.com/conecto-dvr-cctv-pc-como_143567/
In YouTube you will also find tutorials and it will be easier to do it than if we explain it here
regards