What can I do to atone for breaking a covenant I made with Allah not to return to a specific sin, but I have returned to it?

By original Islamic law, one must abandon sin. This obligation is further emphasized by a covenant or an oath. If someone covenants with Allah or swears an oath to abandon a sin and then returns to it, they must offer an expiation for breaking an oath (feeding ten poor people, or clothing them, or freeing a slave; if unable to do so, then fasting for three days). This applies if the covenant was verbal or the oath was by Allah or one of His attributes. However, if the covenant was not verbalized (it was between oneself and Allah), or the oath was not by one of Allah's names, or if there was no intention of an oath accompanying the writing, then what is required is repentance, abandoning the sin, and not returning to it.