Stretch posterior chain
In the above video, Kenny from Physio K shows you how to stretch your posterior chain, which is your low back, your glutes, your hamstrings, your calves and your feet; It's the whole posterior chain. All these muscles are connected via fascia.
Laying on your back on a mat, try to shuffle all the way forward, so our bum is touching the wall. From there, try to keep your knees together, your heels together, your toes towards your nose and from this, in this position, try to push your heels all the way to the ceiling, without losing all the components: the toes towards your nose, knees together and your heels together. Try to stay in this position for about a minute or until you feel a little softening. After that just try and push a little bit higher and keep your toes pointed towards your nose and your knees together. Try to stay in this position for about five minutes in total and that will give you a good stretch of your posterior chain.
This is the best exercise to do for people with short hamstrings and tightness in the lower back. It should be done at least 3 times per week and for at least 5 to 10 minutes per day.