how to sit at a computer
Sit or stand, Keep your spine straight, Pull your head/chin straight back.
Sit or stand, Keep your spine straight, Squeeze your shoulder blades together.
Sit; straighten your lumber curve as much as you can, then slouch your curve.
-Extension from standing:
Stand, put your hands behind your pelvis, move your back backwards as much as you can.
-If you feel any pain stop exercise and ask your doctor.