AT THE REGISTRATION:
At the end of the form, you can chose to define a particular establishment. If your school is a client of Simplyk, you can then choose your group/grade.
If you have already registered, but have not defined your school yet, you can still do it. Go to "my dashboard" and then "my info".
However, if you wish to correct an information already entered, you will need the approval of the volunteering responsible of your school to change your grade.