The lat single arm pull-down is a resistance training exercise that targets the muscles of the back, including the lats, traps, and rhomboids. It is the same movement as the alternating version just focusing on a single side. It is typically performed using a resistance band and a stable surface, such as a door or a pole, to anchor the band. 

To perform the exercise, you will need to grip the band with an overhand grip, palms facing down, and pull it down toward your chest, squeezing your shoulder blades together as you do so. Be sure to keep your elbows close to your body and avoid swinging the band or using momentum to lift the resistance. 

It's also important to use a resistance that is challenging but manageable and to avoid rounding your back or arching your lower back during the exercise.