Access the Course by going to the course from which you want to unenroll students.
Go to the "Participant" Tab within the course.
Select Users to Unenroll if the students or users are manually enrolled, select all the users you want to unenroll by clicking the checkbox next to each user.
Initiate Unenrollment to the previous students by scrolling down to the bottom part of the page.
Click the drop-down button and select "Delete selected user enrollments" under Manual Enrollments.
You will be redirected to the Bulk User Operation page. Click "Unenroll users" to complete the process.
You can now enroll the students you want to add on the course through cohort sync or manual enrollment without deleting the previous contents of the course.