Hi Ivan,
what a coincidence - I am just solving the very same issue with a Czech user in the Czech Moodle community forum. Yeah, unfortunately there is no simple way to let Moodle to recalculate the grades. The thing is, individual grades from peers are calculated and stored at the moment when the assessment form is saved by the student. The only thing you can do now once you have fixed the mapping table is
- Have the workshop in the Evaluation phase
- Use the "Clear assessments" tool. It will mark all submissions as not assessed - yet it does not remove the allocation (who is assessing who) and how the assessment forms were filled
- Switch the workshop back to the Assessment phase
- Let students to re-save the assessments forms (or you, as a teacher/admin, have to go and log in as every student and do that on behalf of them.
I am really sorry about this, I am aware it's an important usability issue and should have been fixed ages ago.