Boruto died by one of the most important people in his life, Sarada.
Ōtsutsuki Isshiki controlled her and killed him when he was the most vulnerable.
At the brink of his death, he activated a special ability of his Kāma seal and went back in time to the point he was a baby.
"I am going to save my family and lovers...I am going to change it all but most importantly. I will kill Otsutsuki clan... I will kill them all!"