How does a Muslim repent from sins that are known, those that are doubted, and those that are unknown?

Sins are divided into two categories: those related to the rights of Allah Almighty, for which sincere repentance suffices, and those related to the rights of people, which require sincere repentance in addition to seeking forgiveness from the wronged party. The door of repentance is open to every person, no matter how great their sins, as long as the sun has not risen from the west or death has not befallen the sinner, for Allah Almighty says: "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" And the Prophet, peace and blessings be upon him, said: "Indeed, Allah, the Exalted and Most High, stretches out His hand at night to accept the repentance of the one who sinned during the day, and He stretches out His hand during the day to accept the repentance of the one who sinned during the night, until the sun rises from its west." And he also said: "Indeed, Allah accepts the repentance of a servant as long as he does not gurgle [i.e., is not on his deathbed]."