Change HDMI-resolution for console in Home Assistant Green?

Installation
1

I have connected a small 3,5" LCD-display with a HDMI-cable to a Home Assistant Green to see the Console/CLI, preferably in resolution 480x320. But the default resolution is way to high, the text is so small that I need to use a magnifying glass to be able to guess what it says.

Is it possible to force a custom resolution like 480x320 in /boot/config.txt with lines like:

hdmi_group=2
hdmi_mode=87
hdmi_cvt=480 320 60 6 0 0 0

If so, where is config.txt in Home Assistant Green? There is no boot directory, and nothing in mnt.
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