I will become an immortal in this world

I was reincarnated as a prince in the Qi Dynasty's palace. Fang Wang had a heavenly palace in his mind, where he could let his consciousness enter and practice. Any technique, The ultimate skill can be cultivated to great perfection, and it cannot be released until it is perfect. No matter how long you stay in the heavenly palace, the reality is only a matter of seconds.
At the age of sixteen, Fang Wang entered the realm of martial arts myths without anyone knowing.
However.
One day, Fang Wang heard that Zhou Xue, the adopted daughter of his fourth uncle, had gone crazy and said in the Duke's Mansion that Fang's family was about to be exterminated.
Fang Wang quietly came outside Zhou Xue's house and happened to hear her talking to herself: "Oh, I guess I am also an immortal after all. Now that I am back to my youth, I can't change the fate of my family. Is God deliberately playing tricks on me... Even if it was a month ago, it would not be like this..."
 The reborn?
 And he’s still an Immortal?
Fang Wang's cognition was broken, and he was shocked but also a little surprised.
 Who can practice martial arts if he can cultivate immortality?
 …
Having traveled thousands of miles across the mountains and rivers of the mortal world, I am only looking for one immortal method in the world that can make people become immortals instantly.