how to recover a group

Hello,
Once a group is deleted the data is gone, it is not possible to roll back the changes.
I recommend you to review the my mailbox (Mi buzón de correo) tab under My Dashboard, it typically keeps the results of your students for 30 days, you can use them to create a back up to try to recover the results.
I hope this helps, let us kn ow if you have any questions.