If an admin schedules an item twice with the same instructor, there is a warning that pops up for the instructor as below:
-Learning Management System
There is an option of giving a warning of conflicting schedules rather than forcing the admin to cancel the previous schedule.
Login to LMS admin--> System admin--> Configuration--> Global variables--> Prevent Resource Conflicts
Once you untick this option, you will only receive warning that you can ignore and proceed conflicting schedules for a instructor
Prevent Resource Conflicts Schedule offering conflict Learning , KBA , LOD-SF-LMS-COR , LMS Core - Items, Catalog, Curricula , Problem