If you would like to add reviewers to evaluation groups or modify which evaluation groups your reviewers belong to, you can make these changes under the People section of the Bonfire Portal. Under the People section, you can see a list of reviewers and a quick summary of which groups they are assigned to.
If you would like to add reviewers or edit the groups they are assigned to, click the Manage button → select Reviewers (shown in the screenshot below)
From the Manage Reviewers popup, you have the ability to add/remove reviewers and assign them to the appropriate Evaluation Groups:
Reviewers aren't able to edit or take over other reviewer's scoring, but you can edit evaluation groups to remove and add reviewers as needed.
Note: For more information on Evaluation Groups, please see the following article: Evaluation Groups