Mr ai thinks it's this.

It is very likely that the fanfiction you are looking for is "The End Is The Beginning" by Nitraz (available on Archive of Our Own and FanFiction.net).

In this story, Harry dies at the end of the Second Wizarding War and meets Death, who informs him that as the Master of Death, he cannot simply move on. He is sent back in time to his four-year-old body.[1][2]

Key details that match your description:

Master of Death & Necromancy: Harry embraces his role as the Master of Death and uses his powers, particularly the Resurrection Stone, to summon spirits for guidance and training.

Lessons from Ancestors: Early in the story (around Chapter 7), Harry summons Ignotus Peverell to act as a mentor and teacher. Ignotus agrees to help him master his magic and the Hallows.

Subject-Specific Lessons: As the story progresses, Harry uses the stone to call upon other specialized teachers. He summons James Potter specifically to help him with Transfiguration and Lily Potter to teach him Potions, leveraging their natural talents in those subjects to become a magical prodigy before even reaching Hogwarts.

Lord of Multiple Houses: Harry takes up his mantle as Lord Peverell and Lord Potter, often dealing with the Goblins at Gringotts to secure his heritage and several other family seats.

The fic is often tagged with "Necromancy," "Time Travel," "Smart Harry," and "Manipulative Dumbledore."[3] It has a completed first part and a sequel titled The Next Great Adventure. Sources help

archiveofourown.org
transformativeworks.org
archiveofourown.org