However, when the Mother of Faces felt the pain in Ursa's heart she offered something extra: not only a new face but a new mind, where all her memories of her life as Ozai's wife would be erased.

Source: https://screenrant.com/avatar-last-airbender-zuko-mother-ursa-what-happened/

With the help of his newfound friends, he must learn to control his powers and put an end to Fire Lord Ozai's () reign of terror.

Source: https://collider.com/avatar-the-last-airbender-show-ending-explained/