AOC 4Vn Pincushion problem function buttons ain't working

[dolescle]

I've got 3 monitors with pincushion problem and the front functio
button for pincushion doesn't work,function buttons work fo
brightness,contrast and other functions but not on pincushio
adjustment...all 3 got the same problem but can't seem to find th
problematic component..can anybody help me with this one..

thanks in advance.