It’s not documented in Github README, but you find the needed config in the implementation here
So…try the following and add the windUnits property.
{
module: "MMM-OneCallWeather",
position: "top_right",
header: "xxxxxx, // OPDATERET HEADER
config: {
latitude: "xxxxxx", // OPDATERET LATITUDE
longitude: "xxxxx", // OPDATERET LONGITUDE
apikey: "xxxxxxx",
iconset: "4a",
iconsetFormat: "png",
units: "metric", // Styrer at vindhastighed er i m/s
fade: false,
windUnits: "ms" //ADD THIS PROPERTY
}
}