Very simple thing is to lay on the floor on your back with the back of your calves resting on the couch or chair... and your butt as close to the couch as you can. Let your hips relax and the weight be on your calves... it'll create some release in your low back. Stay like that for as long as your able.
More active release are Doorway dips. They can help release the hip flexor... sometimes that gives relief.
Stand in a doorwar with your left shoulder against the frame. Raise your left leg like a landing gear and lower your knee straight down toward the floor, bending your right knee. Go as deep as you can, sliding your shoulder down the frame.
Take your left knee as straight down as possible. Keep your right knee over your toes. Dip as deeply as you can. Do a few reps and see.
If the dips are too stressful, you can do a similar thing on one kneewith your right knee on the ground. Put your left foot forward at about a 45° angle and lean your left knee over your left toe... but keep your hips square...
Lol... that's a lot to explain in words. Hope it made some sense