We have replaced their skins with other skins. If you say: How can the skins that have sinned be punished with skins that have not sinned? I say: The punishment is for the sensitive body, which is the one that sinned, not for the skin. And from Fudayl:

He makes the skin that is not roasted different from the roasted one. And from the Messenger of Allah, blessings and peace be upon him: "Their skins are replaced every day seven times." [[I did not find it. And Ibn Adi and Al-Tabarani narrated from Ibn Umar: A man recited before Umar (Whenever their skins are roasted, We replace them with other skins) and Muadh said: They are replaced a hundred times every hour. Umar said: I heard it like this from the Messenger of Allah, blessings and peace be upon him." In it is Nafi' ibn Yusuf Al-Sulami and Abu Hurmuz, and he is weak. And Ishaq ibn Rahwayh said in his Musnad: Fudayl ibn Iyad was asked about this verse, and he informed us from Hisham from Al-Hasan who said: Their skins are replaced every day seventy thousand times.]] And from Al-Hasan: Seventy times they are replaced with white skins like parchment so that they may taste the punishment.

So that their taste may endure and not cease, like saying to the noble: May Allah honor you, meaning may He keep you in your honor and increase you in it, being mighty over them, nothing is impossible for Him of what He desires against the criminals, wise, and He does not punish except with justice for those who deserve it.