Place a resistance band underneath your feet, and grip either side so your hands on the outside of your legs. You should be hinging at the hips, so your back is neutral, knees will be slightly bent and arms striaght.
Drive through your feet, and exhale as you extend your hips. Squeeze your glutes and brace your core at the top, standing tall.
Descend slowly, hinge and push your hips back, engaging the hamstrings. Allow a slight bend in the knees, keep your back neutral, and don't go past the range of your hamstrings.
Repeat for repetitions.
(You can use the edges of your hands for feedback, by pushing them into the crease of your hips.)
Keep your spine neutral, lead the movement with your hips. Your knees can bend further to allow you deeper into the hinge.
Continue until you reach the end of your hamstring flexibility, but do not try to go lower by flexing the lumbar spine, your back should remain neutral throughout the movement.
Push through your heels to drive your hips through. Fully extending at the top, squeezing the glutes. Repeat for repetitions.