How to adjust the screen edge

My os is ubuntu mate 20.110, system is raspberry pi 3b
After boot, the screen can't be seen total, some part is outside.

I google and know how to handle on pi os which edit /boot/config.txt

comment the #disable_overscan=1


I tried it but it did ot work.

How to do in ubuntu 20.10 on raspberry 3b?
I can't see half of bar

I google it . sb. said adjust tv.
menu->piture size ->Direct
Then I see all the bar