What is the path to repentance for having described someone who did not hear me as an "ابن حرام" (haramzade/bastard)?

We mentioned in Fatwa no. 58316 that the phrase "haramzadah" (illegitimate child) is one of the most dangerous insinuations of slander, and one must avoid it, based on the Almighty's saying: "And speak to people good words." It is not permissible to describe anyone with such a term except with clear evidence and proof, due to the defamation of lineage it entails. Repentance from this sin is obligatory, as is seeking forgiveness from the person you described in this way, unless seeking forgiveness would lead to a greater harm.