I think when you have in the connect app and on your watch the settings into metric and into km for like distances, etc. Then the wind speed can be displayed in km/h.
You have to go to user settings and system settings on phone or connect app.
You can also access these setting on the web page of your Garmin connect account here:
Changing the Units of Measure You can customize units of measure for distance, pace and speed, elevation, weight, height, and temperature. 1 Press Menu. 2 Select Settings > System > Units. 3 Select a measurement type. 4 Select a unit of measure. Advanced Settings
