What is the expiation for an evil assumption, and does Allah forgive the rectification of intention in a matter predetermined with ill intention, even if the person continues in the same direction that caused the evil assumption?

You must distance yourself from ill thoughts and the whisperings of Satan, and abandon what causes you doubt for what does not, and think well of others. You must also repent from all sins, for repentance erases what came before it, and Allah forgives all sins.