From the documentation, follow this link and update the row with these

mainAxisAlignment: MainAxisAlignment.center, // Center the row contents and a SizedBox for some space

so it should look like this then

Row(
          mainAxisAlignment: MainAxisAlignment.center, // center  contents
          children: <Widget>[
            Text(label),
            const SizedBox(width: 8), // some spacing between text and switch
            Switch(
              value: value,
              onChanged: (bool newValue) {
                onChanged(newValue);
              },
            ),
          ],
        ),