How can sins and mistakes that are difficult or impossible to rectify be redressed to avoid despair?

The door of repentance is open for every person until the sun rises from the west or death is witnessed, as Allah Almighty said: {Say, "O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah . Indeed, Allah forgives all sins."} And the Prophet, peace and blessings be upon him, said: "Indeed, Allah accepts the repentance of a servant as long as he has not gurgled [i.e., is not on his deathbed]."

A sincere penitent should follow his bad deeds with erasing good deeds. Remorse for sins, abandoning them, and resolving not to return to them, along with restoring injustices, are conditions for the acceptance of repentance.

To strengthen faith and steadfastness, one must read books of encouragement and deterrence, reflect on the Quran, associate with the righteous, and make abundant supplication.