Assuming you have connected the DVR/Cable box with a standard co-axial antenna cable, switch on the box and go to the tuning menu on the TV.
Tuning details are in the TV manual. If you don't have the manual, download here:
When tuning is completed go through the channels to find the cable box. (Note: TV will not tune to the box if it is not switched on when tuning)
If there is still no connection, the DVR/Cable box may need connecting with a composite video cable (red / white / yellow RCA connectors), rather than just a standard co-ax cable.
The connection is at the front of the TV. There is no red connector on this TV so you will have to use an adaptor to connect both left and right (red & white) audio into the white socket. Select AV on the remote control.