First of all you should go for walks in morning or evening, then after walk you should start with stretching your body along with lower back stretch.
Next Steps
Do exercise for your core strengthening like crunches, planks, bridging, lower back isometric holds and hypertension, etc ( need more assistance you can ask me out)
Health Tips
Avoid junk, do not eat too much calories in a single meal, do not do prolonged sitting.