You can revert a build back to setup mode if a test session has not yet been started. To do this, navigate to the build details window, and click the green Released for Testing button. A dropdown should appear where you can select Setup in Progress. Selecting this will put the build back to setup mode.
Note that once a test session has been started, you will not be able to revert the build back to setup up. However, additional requirements/test suites/standalone test cases can be added to the build so that they can be included in future test sessions.
Users will need view and edit permissions in the test coverage module to perform this action. Depending on the settings of a users project permissions, users may be able to view all project builds or just a subset of them. Project owners manage the permissions for project members.