Hi,
Please consider engaging in regular physical activity, resistance training (lifting weights or own body weight exercises) for whole body will help.
For immediate relief from the stiffness you can use a tennis ball / golf ball / cricket ball to roll on the stiff areas of the back and shoulder blades. Follow it up with heat packs and stretching.
Next Steps
physical activity, rolling with the ball or foam roller and stretching, heat packs as part of therapy