You can edit a student's leaving date if they have been unenrolled by mistake.
Go to the Enrolment section of the student's Student Profile. Click on the student's current enrolment into your school.
In the slide over, click the orange Edit button.
Change the information then click Save Changes.
You can also delete the leaving date and remove the leaving reason if the end date has been put in accidentally. Their enrolment will then be extended indefinitely, until you unenrol them again, or they are unenrolled as part of the New School Year Setup process.
Once completed, check if there are any redundant attendance marks and remove them if there are.