How can one atone for the sin of having made a bad supplication against one's mother?

Righteousness towards parents is among the greatest acts of drawing near to Allah, and disobedience to them is among the greatest prohibitions; such as supplicating against them or insulting them, for the Prophet, peace and blessings be upon him, cursed whoever insults his parents. And whoever has wronged his parents by doing so, he must repent and seek forgiveness, ask for their pardon and forgiveness, and treat them kindly. If the mother is alive, he must apologize, show righteousness, and obey her. If she does not know about it, he should not inform her, but strive to be righteous towards her. If she has passed away, he must supplicate for her and seek forgiveness for her, give charity on her behalf, pay off her debts, and fulfill her bequests. Repentance erases what came before it, and Allah forgives all sins for whoever repents with a sincere repentance.