The best way to bulk enrol students from a course is to go to the course, then:
- go to Settings> Course administration> Users> Enrolment methods
- click on the enrol users icon for 'manual enrolments' (it is usually an icon with two faces)
- select the students to unenrol
- select 'Remove'
NB If you have too many users to unenrol, then please use the csv option (search for 'bulk unenrol').