"An indulgence is a remission before God of the temporal punishment due to sins whose guilt has already been forgiven, which the faithful Christian who is duly disposed gains under certain prescribed conditions through the action of the Church which, as the minister of redemption, dispenses and applies with authority the treasury of the satisfactions of Christ and the saints." (CCC 1471)

How does indulgence remit temporal punishment?

"An indulgence is a remission before God of the temporal punishment due to sins whose guilt has already been forgiven, which the faithful Christian who is duly disposed gains under certain prescribed conditions through the action of the Church which, as the minister of redemption, dispenses and applies with authority the treasury of the satisfactions of Christ and the saints." (CCC 1471)

Please correct me if I'm wrong but as I understand it, temporal punishment is the consequence of one's sin. However, it is said that indulgence can remit temporal punishment.How does indulgence remit temporal punishment?

I'll give two scenarios to work on the question:

Scenario # 1

David was forgiven his adultery with Bathsheba, but still he had to endure the pain of seeing the child die.

It is clear that David payed the penalty of temporal punishment. There is no indulgence in this case.

Scenario # 2

Nicolas was forgiven of his promiscuous behavior, but still he had to endure the consequence of his sin which is HIV.

In this scenario, how does indulgence remit the temporal punishment?