There is an instruction called "ent_next(entity)"
please refer to the manual for more information.

Here is the example code rewritten to fit your needs:
Code:

---

define blocked, skill1;

function reset_skill()
{
  you = ent_next(NULL);

  while(you != NULL)
  {
    you.blocked = 0;
    you = ent_next(you);
  }
}

---