Once student hand in their answers, you can see their scores on the "Answers" tab. Clicking on a student name, you will see the answers to the worksheet.
Above the answers, there is an Open/Lock switch which is Locked for students that handed in their responses. To allow a student to re-submit, you simply switch to Open, instruct the student to go to the original assignment link and make corrections.
If you wish the whole class to redo the worksheet, simply create as many assignment links and send to ALL the students. This will keep the old scores.