I have already established my power and prestige, so how did Li Shimin come back to life?

Waking up, he found himself transported to the fifteenth year of the Zhenguan era, and even became the Crown Prince?! Even more astonishingly, his father, Li Shimin, had prematurely "died"? This meant the throne was practically his for the taking—sweet as a feather! Hmph, trying to take the throne from me? Let's see the might of my three great armies first! But who could have imagined that this was all a scheme orchestrated by his father, a test to see who the true Son of Heaven was? However, the "time traveler" wouldn't sit idly by. Watch as he leads his army into Chang'an, purges the powerful clans, implements a major reform, and sets sail! Just as Li Shimin was shocked by his son's audacious actions, he suddenly realized: How come the Tang Dynasty is so powerful now? Oh...