To restart the turn, start with the most recent game action and undo it, then repeat this for each game action taken this turn in reverse chronological order.

If any game actions involve randomizing a portion of the library, randomize it again to undo that action.

If any cards are put into a library to undo an action, and they weren’t known to have moved from a certain position in that library, randomize that library after doing moving those cards.

Any damage undone this way doesn’t count as life gained. Similarly, life gain undone this way doesn’t count as life lost.

While restarting the turn, no abilities can trigger. Abilities trigger when something happens, not when something unhappens.

Do-Over : règles, fonctionnement et interactions (MTG)

Do-Over is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Restart the turn, except with Do-Over in exile. (First, return all cards to where they were as the turn began. For information from hidden zones like the hand, reconstruct as best you can, and do the rest at random.)

How it works : Do-Over

Original English text — Wizards of the Coast / Scryfall

#1November 12, 2019· Wizards of the Coast
To restart the turn, start with the most recent game action and undo it, then repeat this for each game action taken this turn in reverse chronological order.
No other card is named in this ruling.
#2November 12, 2019· Wizards of the Coast
If any game actions involve randomizing a portion of the library, randomize it again to undo that action.
No other card is named in this ruling.
#3November 12, 2019· Wizards of the Coast
If any cards are put into a library to undo an action, and they weren’t known to have moved from a certain position in that library, randomize that library after doing moving those cards.
No other card is named in this ruling.
#4November 12, 2019· Wizards of the Coast
Any damage undone this way doesn’t count as life gained. Similarly, life gain undone this way doesn’t count as life lost.
No other card is named in this ruling.
#5November 12, 2019· Wizards of the Coast
While restarting the turn, no abilities can trigger. Abilities trigger when something happens, not when something unhappens.
No other card is named in this ruling.