If you change a question or its mark scheme after students have answered, you can re-mark the work that was already submitted rather than adjusting marks by hand.
Change the question first
Open the lesson from My Library and make your change: the marks, the correct answer, or the mark scheme. Save it. You will see a note that the question already has submissions.
Then re-mark
Open the classroom from the sidebar, go to Assignments, click the assignment and then the lesson.
A banner offers Re-mark affected questions. Click it, check which questions are listed, and confirm.
Re-marking runs in the background and can take a few minutes for a big class.
What triggers a re-mark
Changing the marks allocated to a question.
Changing which option is correct, or the correct pairs or order.
Changing the mark scheme on a long answer.
Fixing a typo in the wording does not flag anything, so you can tidy up without prompting a re-mark for the whole class.