It naturally tightens back up. Just besure you do you uterine massage the few hrs after birth so you dont bleed to death.
Breastfeeding (at least the first few weeks) helps your uterus go down completely. Exclusive formula feeders have larger uteri after six weeks than do exclusive breastfeeding mamas.
Ok and what is the uterine exercise?
I think that's what the nurses do when you are in the hospital. Push hard on your uterus and it makes more blood come out.