Well, I assume that when this person began their converted life, they made a good confession and included the sin and crime of abortion, and that they were absolved by the confessor. Therefore, I assume they repented for this sin as well. However, if the confessor did not give an appropriate penance, which would indeed be a mistake on the confessor's part, not providing a suitable penance for such a grave sin, then the person could go to another confessor and repent again.
It is possible, even for past sins, to confess them again. Even if they have already been forgiven, we can confess them again, not frequently, of course, as that would lead to scrupulosity, but when we feel the need to repent more deeply, we can occasionally do so. I repeat, not frequently, and we must avoid scrupulosity and a lack of trust in divine mercy, which has already forgiven us. However, to make some reparation, it would be possible to confess the past sin again and ask the confessor for a suitable penance.
Dear visitors of Gloria Dei and all who have already written or who will write a personal message to me. I am grateful for your attention, your kindness, for your spiritual support and especially for your sacrifices and prayers for me. God may reward you!