Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.

 

By just signing a paper or stating that he has already divorced his wife, she becomes immediately divorced. He can revoke this divorce by just returning back to normal relation even without her permission as long as she is still at her waiting period. After the elapse of her waiting period, he must have a new contract by getting two witnesses and a guardian and a new agreement with her on dowry.

 

Almighty Allah knows best.