أَتْبِعِ means “follow [one thing] with [another].” The wording encourages a prompt constructive response to a wrong deed: acknowledge it, repent, and take meaningful corrective action.
If another person’s rights were violated, extra voluntary worship or charity does not substitute for returning property or making appropriate amends. If you damaged another student’s book, compensation is part of repairing the wrong.
السَّيِّئَةَ (“bad deed”) and الْحَسَنَةَ (“good deed”) are feminine singular nouns. This helps explain the feminine verb and pronoun in تَمْحُهَا.