When all of the knowledge areas in an assessment are complete, the assessment page will have a COMPLETE button under the progress bar.
Marking an assessment COMPLETE locks the entire assessment and prevents any further changes being made. This should only be done once you are sure that the assessment is finished with and CANNOT BE UNDONE.
The full results can only be viewed for complete assessments, so it is essential to complete the assessment before trying to review results. See Understanding the assessment results for more information.