In order for a Teacher to see the 'Manage' button in the roster of a course they teach:

If no onRecord products are installed, the Manage button appears on the roster.
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If any onRecord product is installed, there is no Manage button for teachers to manage their roster and this is NOT an Available Option.
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If you have onCampus Only and you are not seeing the Manage Roster Button, then as a Platform Manager navigate to:
  1. Core > Users/Access > Profile > Manage Roles > Teacher > Tasks'
  2. Click the 'Edit'
  3. Mark Manage Course Roster to turn on or unmark to turn off
  4. Click Save
The 'Manage Course Roster' task in the Teacher role

*It is common for some schoolsto rename the Teacher role to the Faculty role