Zenith tv picture is larger than screen
There are Horizontal and Vertical size controls behind the back cover that need to be adjusted using a hand held tool. This adjustment requires a trained tech. High Voltage from the set is dangerous.
However, there maybe some limited controls that may help through the on screen menu.
To get into the setup menu, you need the original Remote that came with the TV.
Hold the Menu Key down until a box appears in the corner of the screen, then press 9,8,7,6 Enter. this takes you to the service menu. Just scroll through the items to find Horiz Size and Vert Size.