Foam roller for myofascial massage, longer the muscles surrounding the injury stay tight the worse they get.
Roll every night and if needed a gently stretch in the mornings after a hot bath/shower.
I personally use a basketball rather than a roller as its harder and gets my tight bits better. Roll either side of the spine not directly on it.
Try this stretch for lower back, don’t force it relax the muscles and breath..
If its lower to mid back, bring the knees higher up towards the chest and stretch.
Stretch in post above is a piriformis stretch, if these get tight they can cause lower back pain/issues, you can also roll the glutes and get the piriformis