Apocalypse Cheater Novel

What would happen if a man happened to travel back into the past where he can undo his mistakes and regret? Near in the future, an unknown being appeared and claimed that a new reality shall be opened up for humans to enter, creating havoc across the world.However, what they didn't know is that 10 years later, monsters from the unknown void broke through the world and caused massive destruction. The powers obtained from that reality can be brought out to the real world, hence, Earth could defend itself from these monsters.However, another 10 years later, Daniel Bell has been killed by a bunch of monsters, and suddenly he has travelled back to the past. Is this a fortunate outcome or will history repeat itself? Only the future can tell.