Let students mark a course as complete. This block works with the Course Completion tracking settings in a course and requires that a teacher has enabled manual completion for the course.
The Self Completion block contains a link to manually set the completion status of the course for the student.
A course cannot be set to incomplete by a student after it has been marked complete. The Self Completion block will not show up for a student who has already marked a course as complete.
A teacher can delete completion status for all students in a course. Only all students' completion status can't be reset for individual students. If this happens, the Self Completion block will reappear in the course and each student will need to manually mark the course as complete again.
More on the Self completion block on the Moodle website (may be available in English only)