I don’t think a philosopher or at least a Socratic one would necessarily think of the soul in terms of “good or evil.” I think Socrates viewed the soul as either choosing or acting in ways that are right or wrong. He believed that no rational person or soul would willingly choose to do wrong (evil) because harm would always come upon him or her from doing so. If people do something that is wrong, they do it out of fear and ignorance.
Socrates claimed to live a good or right life. I think he did it to purify his soul in order to break away from the reincarnation cycle where doing/thinking wrong just keeps you trapped in. So if we choose to live a life pursuing wisdom and the knowledge of what is true and right, we then can all eventually break free. That’'s my interpretation of what Socrates believed about good, evil, and the soul.
[Very lightly edited to enhance readability -TT]