Fixing overscan on an uncooperative TV-monitor

This is mainly so I can find this again and not have to rediscover this for the third time after I forget. I can't find this exact solution anywhere else so I figured I should put it somewhere.

I have a terrible Insignia tv that locks the overscan option so you can't even turn it off, and linux mint for whatever reason doesn't recognize it as a TV so I can't use their automatic TV adjustments. This is just for x11 afaik.

So in the end, I used the underscan to defeat the overscan and it works great:

xrandr to get the output name the TV is using, then

xrandr --output <name-of-tv-output> --set underscan on --set "underscan hborder" <0-128> --set "underscan vborder" <0-128>

to enable underscan and tweak the border values which squash the edges of the screen, undoing the effects of the overscan.

for me the optimal values are 128h 40v but you can just experiment by typing the command into the console before you make it permanent.