Set android display resolution

I have a new haven display that runs 800 x 600. https://newhavendisplay.com/5-0-inch-ips-capacitive-hdmi-tft-module/

On my previous SBC’s running android I needed to configure the screen size manually. To do this on my other devices I would just edit.Env.in. Since I am using a rock pie 4 b+ I don’t have access to that file since it’s onboard emmc Is there another way to configure the display resolution? Can I mount the emmc via usb OTG?

Currently when it boots the screen is flickering, so I’m unable to use the GUI to set the display settings.
Thanks

Any help on this?