What is the way out of the sin resulting from designing and constructing buildings that are highly likely to be used for unlawful purposes, and how can one absolve oneself from this involvement after it has occurred?

If you repent to Allah with sincere repentance, then you will not be held accountable for the sins that occurred or are occurring in those buildings, for Allah Almighty says: "And whoever does evil or wrongs himself then seeks forgiveness of Allah will find Allah Forgiving and Merciful," and His saying: "But whoever repents after his wrongdoing and makes amends, then indeed, Allah will accept his repentance. Indeed, Allah is Forgiving and Merciful." And the Prophet, peace and blessings be upon him, said: "The one who repents from sin is like one who has no sin," and this includes all sins.