Grab the end of the landmine and stand perpendicular to the bar.
Lift your inside leg and keep your outside leg planted.
Push your hips back keeping your knees mostly extended. When you feel the stretch in your hams, push your hips forward until you are standing upright.
Guía de Ejercicio Landmine Single Leg Romanian Deadlift - Entrenamiento de Glutes | MuscleWiki