Is the scribe considered cursed and bearing an ongoing sin until the Day of Judgment, knowing beforehand that the lines he wrote will be used for tattooing, and how can he repent and nullify this ongoing sin?

Repentance from the sin of assisting in tattooing is sufficient to erase its effect, and the persistence of its effect does not matter after being unable to prevent or remove it. The majority of the scholars of Usul (principles of Islamic jurisprudence) hold that repentance is valid because the penitent has done everything within their capacity, and they are excused for what they are unable to do, as Allah Almighty says: ﴿Allah does not burden a soul beyond its capacity﴾.