You can set a default Organisation Unit within an Organisation. When new User accounts are created, and no Organisation Unit is specified, they will be created within the default Unit.
Navigate to Organisation and Users via the Menu.
Alternatively, click User Admin from the Common Tasks Portlet on the homepage.
Click the Organisation you want to set the default Organisation Unit for.
Click the Settings & Configuration tab.
Under Configuration, click Edit next to Default Organisation Unit Code.
Enter the code for the Organisation Unit you wish to be the new default. When you start typing, the LMS will suggest existing codes.
If you don't know the code, you can find this in the Details tab of the Organisation Unit.