Laws are copied in, comments are in-line and bold.

LAW 63 - ESTABLISHMENT OF A REVOKE
A. Revoke Becomes Established
A revoke becomes established:
1. when the offender or his partner leads or plays to the following trick (any such play, legal or illegal, establishes the revoke).
Neither West or East has played to the trick immediately following the revoke, this does not apply.
2. when the offender or his partner names or otherwise designates a card to be played to the following trick.
Neither West or East has designated a card to be played (typically calling a card from dummy).
3. when a member of the offending side makes a claim or concession of tricks orally or by facing his hand or in any other way.
Neither West or East has started a claim/concession.
4. when agreement is established (as per Law 69A) to an opponent’s claim or concession; the offending side having raised no objection to it before the end of the round, or before making a call on a subsequent board.
Neither West or East have agreed to a claim by South.

None of these apply, so the revoke isn't established. Hence you look at the following rule:

LAW 62 - CORRECTION OF A REVOKE
A. Revoke Must Be Corrected
A player must correct his revoke if attention is drawn to the irregularity before it becomes established.
Attention was drawn to it, so it must be corrected
B. Correcting a Revoke
To correct a revoke the offender withdraws the card he played and substitutes a legal card.
West needs to play a / their Spade
1. A card so withdrawn becomes a major penalty card (Law 50) if it was played from a defender’s unfaced hand.
West's Heart becomes a Major penalty card (they freely chose to play it) 
2. The card may be replaced without further rectification if it was played from declarer’s [subject to Law 43B2(b)] or dummy’s hand, or if it was a defender’s faced card.
C. Subsequent Cards Played
1. Each member of the non-offending side may withdraw and return to his hand any card he may have played after the revoke but before attention was drawn to it (see Law 16C).
So South can optionally choose to change which card is played from dummy (now that West has replaced their H with a S). 
2. After a non-offender so withdraws a card, the player of the offending side next in rotation may withdraw his played card, which becomes a penalty card if the player is a defender (see Law 16C). 
Only if North changes their card, does East also get the choice to replace the card they play. If they do, their originally played S becomes a penalty card (it was deliberately played and the existance of it arises from an infraction of their side).
3. If both sides revoke on the same trick and only one side has played to the subsequent trick, then both revokes must be corrected (see Law 16C2). Every card withdrawn by the defending side becomes a penalty card.
D. Revoke on Trick Twelve
1. On the twelfth trick, a revoke, even if established, must be corrected if discovered before all four hands have been returned to the board.
2. If a defender revokes on the twelfth trick before his partner’s turn to play to the trick, Law 16C applies.
This would supercede the above, assuming it's on trick 12 

Hopefully this clarifies the situation for you :)

Thank you Brad, that is very clear.

Helene