Galaxy Watch 6 has over 100 workout modes with various custom settings. You can choose any exercises for your daily fitness session including HIIT workouts. Still, if you want to set up interval training on Galaxy Watch 6, then you can also do it. You can use custom training to add your specific goals and targets. You have to open activities from the given list to enable the training.
For that, on Galaxy Watch 6 or Watch 6 Classic, start a workout like running or cycling. After that, you will see the Setting icon, tap on it. Here tap on Target, and enable the option. Now scroll down below to activate the Interval training options. You can also pause your workout when you finish the target. More options may come to Galaxy Watch in other updates.