Choose three of the themes you see an obvious presence (ie; racism, prejudice, and if it’s a choice, I’d add experience) find a few quotes that present those themes and write away.

If you go this route, try a thesis something like: Harper Lee helps the reader understand that even the negative aspects of prejudice and racism lead to a more experienced person who is more capable of having a positive impact on others.

Use your support paragraphs to present the first place where the theme is introduced (use actual quotes or paraphrasing) and then show that even though it’s early in the novel that it’s having an impact on characters/changing them (use more actual quotes/paraphrasing).

Good luck. I’m not a big fan of having teachers talking about the “exploration” of a theme so early in the text, but one has to do what one has to do.