To implement the test case review system across the organization, an important process would be to grant permissions to a role that will be assigned to the reviewers.

In TestCollab by default all the administrators will have the reviewer rights.

For other users who have limited rights (rights governed by user roles), you can either create a new role or edit an existing one to grant the permission to "review and approve test cases". The permission can be granted or revoked for any of the roles.

Once the "Can review and approve test cases" permission is granted for a role, the users added to projects with the role would have the rights of a reviewer in that project.

Also, please make sure that "Edit any test case" permission is also granted along with "Can review and approve test cases".

For more details on user roles management please check this article.