To do Plank Scorpions, set up in a plank position from your forearms. You can do this from either your knees or your toes. Whichever you do, make sure your body is in a nice straight line from your head to your heels or knees. Engage your core and line up your elbows under your shoulders. Bend one leg to 90 degrees with your foot up toward the ceiling.
Then kick your foot back over yourself toward the ground on your other side. Rotate your foot over with your core while keeping your hips up and your elbows on the ground. Do not let your butt go way up in the air as you rotate either.
Then come back to a front plank and place that foot back down onto the ground. Bend the other knee to 90 degrees with your foot up toward the ceiling. With the knee bent, twist the other foot back over behind you.
Alternate kicks behind you until all reps are complete. Feel your abs working to help you twist and kick the foot behind you.
You do not actually need to touch your foot down behind. Just focus on rotating without your hips sagging or your butt going up in the air.