Heaven and Earth didn't transform the dark metal. They had changed its nature by affecting it with their world. They had corrupted it by modifying the dragons, but Noah guessed that he could partially revert that as long as he removed the rulers' influence.
Noah didn't want to change the dragon's body. He planned to invade its existence and destroy the parts affected by Heaven and Earth. In theory, the process would allow the dark metal to regain its natural properties.
That approach had two problems. First of all, Noah didn't know if the dragon would survive the procedure since it would lose part of its existence. The dark world could help it fill some blank spots, but the difference in the quality of energy could affect the outcome.
The second problem involved the tools that Noah had to use to perform the procedure. Heaven and Earth's influence would be his opponent, so he had to rely on a form of energy that could invade the dragon's existence and defeat that power.
