So there's this stretch I know. It's performed while standing. You get into like a partial sat position, imagine you were trying to hover over a manky toilet but you had to go. So once you're in the half way to taking a dump position, place your hands on your upper thighs, then push down on your thighs with your hands. Start light to see how it goes for you. The theory is that it allows you to lengthen your own spine by pushing your shoulders and hips away from each other.
I’ve done this injury at gym too many times. Osteo massage speeds up recovery. I have a massage gun and use that to loosen the lower back up. Otherwise it’s just time.