If HIIT is not available on the watch, use Cardio, and change the activity type to HIIT after saving, in Garmin Connect. Alternatively, you can also use a Connect IQ app, such as the "Any Activity" for diverse activity profiles not available directly for the watch. Yet another option is copying the HIIT activity profile from another watch model supporting it. It is in the folder //GARMIN/Sports/ on the watch.
