People commonly do this exercise with a cable machine, but you can do it without one as long as you have a band and bar where you can hang it.

Double the band over the bar so that there are two handles for each hand. Grab the bands with a double underhand grip about shoulder-width apart.

Then think of it like a standing crunch. Round your back, contracting your anterior core and rolling your elbows past your midline. Doing it in a standing position carries over to more of your lifts.

Do 4 sets of 25-30 reps once or twice per week. Training the core with resistance has a huge carryover to your deadlift and will protect your lumbar when you're using maximal weights.