How does a person repent from something they do not know?

General repentance suffices for a forgotten sin, as there are prophetic supplications that encompass all wrongdoings, such as: "O Allah, forgive my sin, my ignorance, my excess in my affairs, and what You know better than I. O Allah, forgive my jesting and my seriousness, my unintentional mistakes and my deliberate ones, and all of that is with me." However, if the sin pertains to the rights of others, then one must seek their absolution.