Karabiner-Elements config to change section key § with accent key ` put it into ~/.karabiner.d/configuration/karabiner.json

karabiner.json

{
    "profiles": [
        {
            "name": "Default profile",
            "selected": true,
            "simple_modifications": {
                "non_us_backslash": "grave_accent_and_tilde"
            }
        }
    ]
}