DietPi won't output after changing screen resolution in config program

Originally it ran 1920x1080 just fine, but I think it was bit taxing so i lowered it to 720p via dietpi-config. I tried some basic solution by taking the mSD card and editing config.txt like adding


or force changing to a resolution like

hdmi_group=1 hdmi_mode=20

and it would get a very large screen with extremely low dpi/res (i suppose the boot screen) with white text for few seconds and then the monitor would show no signal. Everything else seems to work as I use it to bridge WiFi to Ethernet to my main PC and works. (RP3 Model B)