Fantasy: Immortals only accept female disciples

A powerful immortal expert decided to sacrifice himself to save one of his disciples. In the end, he was dragged into the endless dark abyss.

However, he was inexplicably moved by the Heavenly Dao. Obviously, the Great Dao itself wanted to use his life and soul to show him the true meaning of the Dao. However, when he thought of his loved ones, he would not rest until he died, defying the Heavenly Dao.

Later, when he woke up, he found that he was still alive, but he had obviously fallen to a lower plane, a small world. There were few Qi spirits there, and there were demon beasts attacking a city that seemed to be the only possible human settlement.

However, his cultivation was still there. It was just that it was now restricted and sealed by the same Heavenly Dao. In short, he had the Heaven Seal, which restricted almost all of his power.

What should Ling Tian do to return to the Immortal World and slowly remove the Heavenly Seal so that his cultivation and strength could return to him?