The ʿiddah has ended but we want to reunite. What must we do?

After the ʿiddah of a revocable talaq (raj'i) ends (or after khulʿ/fasakh), the couple need a new marriage contract with a wali, two witnesses and a new mahr, as well as the wife's consent.
Allah forbids guardians and others from preventing a woman from returning to her former husband when they agree on reasonable terms. This differs from rujuk during ʿiddah, which needs no contract.
In Malaysia, the new contract is registered like an ordinary marriage through the religious affairs office. Make sure the number of remaining talaq is clear; after three talaq, a new contract is invalid without a marriage to another man first. See rujuk & remarriage.