One of our biggest debates was how to deal with lesson scores on re-attempts. After many discussions with teachers, we realized that retaking the same question is not nearly as valuable as giving a way for students to demonstrate that they genuinely understood the answer (and did not simply memorize the correct one). Our solution for this is that on the second go around, students can write in an explanation that demonstrates an understanding of the material. You can then, on the monitoring page, through the slider assign half a point or a full point to their explanation.
If this option does not satisfy your use case, then you can remove the student's answers so that they can retake the questions. Simply go to your Monitor tab and click the X next to each student's answer in the Question by Question breakdown.