We need a complete sentence to answer your question. But, I often use that phrase to my students when I teach in private school like this 間違ったところがあったら、おしえてください。It means Please let me know any mistakes that you have made. 間違ったところは、赤ペンで正解を書いておきましょう。Lets write a correct answer with a red pen where you have made a mistake. Or, in an exam you can see a sentencen like 次の文で、間違ったところがあれば、抜きだし、正しい答えを書きなさい。 In the following sentence , if you find any mistakes write them and the correct answers on the answer sheet.

hi 間違ったところ means a mistaken part